A Croatian programmer's prayer book app hits #1: no ad spend, he built 40k followers first

2026 Oct 12 is the feast of St. Carlo Acutis, the Italian teen who died at 15 and was canonized 2025 years later, now called the patron of programmers. That day, software engineer Zdravko Ćurić, near Split, posted on Facebook: "After two years of planning and work, on the feast of St. Carlo Acutis, I can finally release 'Zrno gorušice'." Zrno gorušice is Croatian for "mustard seed," a Catholic prayer book app. Three weeks later, on Nov 5, it was #1 in the Croatia App Store Lifestyle free chart and #21 overall free. This piece covers how it got there, and why the people it brought in weren't drawn by the app itself.

What it is

A Croatian-language prayer book in your phone: 1200 multiple prayers, 150 litanies, 100 novenas, 15 rosary formats, plus daily Mass readings, saint biographies, a liturgical calendar with name days, and examination of conscience and confession prep. The author says he built a digital version of "Biserje svetoga Ante," the paper prayer book found in nearly every Croatian home.

Compared with paper books or prayer sections on websites, it adds one thing: prayer plans. You pick which prayers to say each day, schedule them by weekday, and set reminders. Novenas get checked off day by day. The author's original goal was exactly this. He told the Croatian Catholic Network (HKM): "I wanted the app to remind me of these prayers every day so I wouldn't miss them. I often do, because I'm forgetful."

All prayer content is free, usable without signing up, mostly readable offline, and ad-free. People who want to pay can become "Supporters": €3.99 a month, €35.99 a year, or €99.99 lifetime (per the official terms). That unlocks unlimited prayer plans, adding your own prayers, 13 color themes, and PDF printing. The content itself is never locked.

What happened in three weeks

The app went live on Oct 10. Daily rating counts for the Croatia store (App Store):

80 global ratings, average 4.94, Croatian only. On Google Play it has 5K+ downloads (11-06).

Seventy-some ratings sounds small, but compare it in the same market: Nova Eva, the longstanding Croatian-language prayer app, launched 2013 years ago and collected 111 Croatian ratings over 13 years. Hallow, the top global Catholic app, has 128 ratings in Croatia. Zrno gorušice hit 77 in under a month, and gained 24 in the last 7 days.

And the money? 11-03 It reached #12 on the Lifestyle top grossing chart. Croatia has only about 3.9M people, so the bar for that chart is low. Reaching it does show people bought supporter tiers, but the volume won't be large (inference). The author's hopes are modest: the app costs about €500 a year to maintain. "If supporters can cover that, I'd be very happy" (Vjerujem.hr, 10-12).

Where users came from: the account first, then the app

The answer is in the name. "Zrno gorušice" was first a social media account, and only later an app.

About a year ago, Ćurić started posting short videos on Instagram, YouTube, Facebook, and TikTok: sermons from American priest Mike Schmitz and clips from American Catholic podcasts, with Croatian subtitles. Later he added sermons and catechesis from Croatian local priests. He told HKM: "The account grew fast, about 40k Instagram followers and 10k YouTube subscribers in about a year, and a WhatsApp channel with nearly 4,000 people." (These are his own figures, not independently verified.)

He's blunt about using the same name for the app: "I'd thought of other names, but I already had a platform people knew." Users now shorten it to "Zrno": "I prayed on Zrno."

In a country of 3.9M people, a 40k-follower Catholic content account already ranks in the top tier. On a small country's Lifestyle free chart, a few thousand downloads in the first few days is enough to climb (inference).

The second channel was church media. Three pieces, all long features rather than news briefs:

• 10-12, Vjerujem.hr (the faith section of Croatian daily Večernji list) republished the author's launch post in full;
• 10-15, an interview with Bitno.net. The author had built their website since they launched, so they're longtime collaborators;
• 11-03, a long HKM interview (the Croatian Catholic Network, whose site runs the Catholic radio station), titled "Father of five builds an app with 1200+ prayers." Two days later it reached #1 on the free chart.

Early November is packed with All Saints' and All Souls' Day, among the busiest prayer stretches on the Catholic calendar. 11-02 also shipped a 1.5 edition with lectio divina guidance. How much of the climb to #1 comes from press coverage, the holidays, and the new release is impossible to tell from the outside.

No paid acquisition seen. The author runs it as a public-good project, costing €500 a year, and doesn't look like he's spending on ads. The other thing he did is a long-term play: the website molitvenik.app turns every prayer, every novena, and each day's saint into public web pages. Searching "Catholic prayer app" in Croatian already ranks it near the top.

Why people stay

The account and media brought people in; the app itself is what keeps them and earns five stars. Reviews posted on the official site (App Store / Google Play, mid-October):

"Exactly what Croatian Catholics have been missing. My favorite is the prayer plan: I can schedule my prayer life and get reminders at the right times." (App Store, 10-17)

"The best electronic prayer book I've seen in Croatian. No ads. The images, fonts, and look are all at a very high standard." (Google Play, 10-17)

"Our whole family installed it, young and 'old.'" (Google Play, 10-19)

"I reported a problem, got a reply the next morning, and the app was updated the day after." (App Store, 10-16)

"I'm praying much more than before, which is exactly what I wanted." (App Store, 10-18)

These reviews point to how it differs from rivals:

• Local old apps are stuck a decade back. Nova Eva is from the 2013-year generation: it has prayers, sermons, and scripture reading, but no personal plans or reminders. The others (Molitvenik i kalendar, Sveta Misa) are small personal apps with a few dozen ratings and narrow content.
• Big players don't do small languages. Hallow has meditation audio and a premium subscription, and Laudate is free with ads. Neither has Croatian, let alone Croatian name days, local saints, and a local calendar.
• "No ads" is itself the selling point. The author wrote in his launch post that many Catholic apps have been ruined by Google's intrusive ads: "There will never be any here." In this audience, that line works.
• Daily readings are licensed. The Croatian Liturgical Institute allowed him to reproduce the daily Mass readings "without reservation." Full Bible text and Liturgy of the Hours are not yet available because of copyright. The license is the part others can't easily copy.
• One person plus AI. The author says he gave up several times. When Claude Opus 4.5 came out late last year, he got motivated again, but "at that point AI did more harm than good," so he stopped again. It took two years total. Now design, testing, translation, and bug fixes all use AI tools, and in three weeks after launch he shipped 1.4, 1.4.2, and 1.5 versions.

How many people know about it

Only inside Croatian Catholic circles. Three church outlets covered it. No tech or international press. Nothing turns up on X, and revenue isn't public. Outside Croatia it has only appeared at the tail of Lifestyle charts in Austria, Slovenia, Finland, and Germany, apparently from Croatian diaspora. No one seems to have copied it yet.

If it were you

C. The playbook is worth studying, but copying it is unlikely to earn much money, and the thing that made it work, a trusted same-name content account plus long-standing church media ties, outsiders can't get.

Who it suits: People already inside a small-language faith community, ideally already running a religious content account (even a few thousand followers) and able to work with national church media and parishes. The goal is a long-term, dignified public-good product that covers its costs, not a business. Languages worth a look: Slovene, Slovak, Hungarian, Lithuanian, Czech, and similar markets with sizable Catholic populations, no Hallow coverage, and aging local apps (check existing competitors in each country first).

Who it doesn't suit: Outsiders hoping to arbitrage "small language + faith": without an identity or an account, church media won't write long features for you, and users won't trust a prayer book from a stranger. People wanting meaningful income: a #12 top grossing spot in a small country probably means a few hundred euros a month (inference), and this audience is sensitive to ads and fees. People targeting big languages like English, Spanish, Portuguese, or Polish: those are dominated by Hallow, Laudate, and mature local products.

How to build it: Account first, then app. Spend a year posting subtitled clips and local-priest videos in the local language to build the audience into the top tier of the local Catholic community. Launch the app under the same name. Organize the content around the country's most common paper prayer book. Core features: prayer plans, reminders, novena check-offs, and widgets. Apply to the national liturgical body for a license to reproduce daily readings. Keep everything free with no ads. Sell "Supporter" subscriptions and one-time lifetime purchases, which unlock only appearance and convenience features. Turn each prayer into a web page to catch search traffic.

How to get users: Pick a launch day that means something to this community (a patron saint's feast, the first Sunday of Advent, Ash Wednesday). Publish the launch video and a long post on your own account. The same week, pitch the author's story to national Catholic media and Catholic radio: sell the person, not the features. After that, follow the church calendar: All Saints', All Souls', Advent, Lent. Before each one, update the matching content (novenas, prayers for the dead, Lenten plans).

When to bet on it: Lent 2027 starts on Ash Wednesday, Feb 10, and prayer apps peak in the window before it. If you already have an audience, ship the app before early February. If you don't, start the account today and hold off on writing code.

Signs we called it wrong: ① Hallow or another big player adds Croatian-adjacent languages like Croatian or Slovenian, and the gap closes; ② Zrno gorušice's media spike fades and it stops climbing: by late December the Croatian store has fewer than 100 ratings and has dropped out of the top 50 Lifestyle, meaning the press drove one-time installs and no retention; ③ The reverse: if it holds a top 20 spot on the Top Grossing chart through December, or the author launches other language versions, small-language prayer apps monetize better than we estimated and the grade should go up.

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Data and sources: Croatian store chart and rating counts (10-28 to 11-06, daily); App Store Croatian reviews (10-14 to 11-03); Google Play page (11-06); Vjerujem.hr / Večernji list (10-12, the author's launch post in full), Bitno.net (10-15), HKM (11-03) coverage; molitvenik.app website, terms of use and changelog (11-06). Anything marked "inferred" is our inference; social follower counts are self-reported by the author.