16 ratings, #1 on the Taiwan Top Paid chart: a Korean office worker's "When Did I Last" got there on one Apple Taiwan feature

A small tool a Korean developer built after work: no to-do list, just "the last day you did this thing," showing how many days have passed. It launched in August, has only 16 ratings worldwide, yet at the end of September it hit #1 on Taiwan's App Store overall Top Paid chart, and from late October into early November it held #1 on Taiwan's Top Paid Productivity chart. Apps like this have existed for 2012 years, and 2026 saw more than 30 new ones. It broke out not because it had new features, but because it suits Apple Taiwan editors' taste, and in regions like Taiwan, Hong Kong and Japan, a few purchases can put you in the top 10 of the paid charts. Below: what it is, where the volume came from, how much it could earn, and which parts are worth copying.

Built by one person, updated after work

In November 5, the developer posted an apology on his own Threads account, @when.did.i: updates had been slow because he worked during the day and took on a research project, so he was building the app after hours while still learning. "I'm really sorry, I won't miss any of your feedback." Around the same time he posted again: "Is my exposure dead? I want feedback, but there are no reviews or DMs anywhere."

The account has 332 followers, and the English account @when.did.i.en has 71. He is HyunWoo Lee. The store developer name is a sole proprietorship, Aslla Soft, and this is its only app.

App 在韩国叫「언제했지」(我什么时候做的),英文叫 When'd I,台湾区叫「上次是什麼時候 - 家事·保養紀錄」。商店页第一句是:

Stop managing to-dos. Just remember when you last did it.

The examples in the listing are "When did I last wash the sheets?", "When did I last change the filter?" and "When did I last call my parents?" There are no goals, no nagging notifications, no checkboxes. One tap records it as today. Each item shows "N days since last," and the spacing between dots on the timeline is the real time between entries: dense when you're busy, a blank stretch when you've neglected something for months. Each entry can carry a photo and a line of text, and monthly and yearly recaps can be exported as images to share.

One-time purchase: ₩4,400 / NT$90 / $2.99 at launch, with no in-app purchases, no subscription, no ads, no account. Data stays on the phone and can sync through Google Drive. It launched on the App Store in August 20 (Google Play came first, on August 15). By November 2 it was at version 5.1.0, with a release roughly every week, and it supports 15 languages.

September 25: Apple Taiwan featured it

For the first month it barely moved. The turn came at the end of September (the early timeline below comes from the third-party chart site AppInsider):

• 9-24: first appeared on Taiwan's overall Top Paid chart at #8; Korea's overall Top Paid at #94.
• 9-25 to 9-30: Apple Taiwan's App Store "Apps" tab featured it for six days straight.
• 9-27: #1 on Taiwan's overall Top Paid chart, and the same day #1 on Japan's Top Paid Productivity chart; Australia, Canada, Indonesia and Thailand's Top Paid Productivity charts placed it in the top 10.
• 10-12: the Taiwan listing was renamed, adding "家事·保養紀錄" (household & maintenance log) after the title, packing in two terms Taiwanese users search for.
• 10-31 to 11-04: Apple Taiwan's second round of features. On 10-31 it reached #2 on Taiwan's overall Top Paid chart.

9-24, before the feature, it was already at #8 on Taiwan's overall Top Paid chart. I couldn't find who first pushed it. 9-27 one Taiwanese five-star review reads "saw it on Threads and downloaded right away" and says "logging when I changed contact lenses, or other routine things, is really useful, goldfish brain saved". I infer a Taiwanese Threads post kicked off the first wave, but I couldn't find the original post.

Daily chart positions from 28 to 6:

16 ratings worldwide. Reaching #1 on Taiwan's Top Paid Productivity chart didn't require many buyers.

On Android, volume is basically nil: as of 11-06, Google Play shows 163 cumulative installs. From late September to mid-October it hit the top 100 of the paid productivity charts in the UAE, Indonesia, Mexico and Vietnam stores (their paid charts have a lower bar), then 11-02 fell off every chart.

How much it could earn

Revenue isn't public. AppInsider estimates its global downloads at "100+ per day" (a rough tier). Assuming a few dozen to over a hundred paid downloads a day at #1 on Taiwan's overall Top Paid chart, at $2–3 each, peak monthly revenue would be in the low thousands of dollars (inferred, unverified). Once the feature ended, volume dropped: by 11-06 it was at #63 on Taiwan's overall Top Paid chart, and it had fallen off Korea's overall chart.

One detail that also eats into revenue: on November 4 he wrote on Threads, "just found out there's a Family Sharing feature that was turned on." For a one-time-purchase app with Family Sharing on, one buyer means the whole family can use it.

Raising the price after charting

From November 2 to 3, while the second round of features was still running, he raised prices in every store:

Increases of 33% to 75%. After the increase, Taiwan's overall Top Paid position dropped from 13 to 63 and Korea fell off the overall chart, but the feature also ended at 11-04, so the two effects are hard to separate.

Who it's competing with

This category is old and crowded. Searching the App Store for "last time / days since / 上次 / 언제했지 / いつやった" turns up 100+ apps. Between August and November of 2026 years, 30+ new ones launched, mostly in English with a free-plus-in-app-purchase model, and none targeting Asian languages.

Neither Apple nor Google has a native "N days since last time" feature. You can only make do with Reminders and Calendar, which is why this category keeps getting built and keeps getting bought.

Compared with Last Time Tracker, its core features are not very different. What sets it apart is three things: Traditional Chinese, Japanese, and Korean that read like they were written by locals; a clean interface; and a price half as high. These three things earned it a recommendation from Apple's Taiwan editors, but the volume comes from editorial picks and low-barrier paid charts, not from users spreading it on their own.

Why users buy it

Reviews keep repeating three things: it's simple (one tap to log), there's no pressure (it's not a to-do list, so missing something doesn't cause guilt), and you can look back (photos and a timeline). One Korean user said they're a "record maniac", and that logging too much made them forget "what I should do and when I last did it"; this app "solves it with a light tap". A Taiwanese user 11-04 commented that iCloud couldn't sync across devices, and only switching to Google Drive worked.

The developer personally replies to comments on Threads, shows off chart climbs, and responds to bad reviews. One 2-star user complained the black-and-white look was too plain, so he made 11 color schemes and "gave them to you". He doesn't have many followers, but it counts for a lot with Asian users.

The five-star reviews in the Korean store from around September to early October read like heavy promotion, similar to people in Korean developer circles downloading and writing praise for each other. There's no direct evidence.

If it were you

C: This playbook is worth learning, but building another "N days since last time" app by copying it isn't worth it. The category already has 100+ competitors, and 2026 years on it's still adding nearly 10 a month. Its own volume came from two rounds of Taiwan App Store recommendations. When the recommendations stopped, it dropped off the charts. At peak, the estimate is only a few thousand dollars a month.

Who it suits: a solo developer making iOS utilities, whose native language or second language is Traditional Chinese, Japanese, or Korean, who is willing to do a one-time purchase rather than a subscription, and who treats this as a practice project for learning how to earn Apple's small-storefront recommendations. Or someone who already has a clean small tool and just hasn't localized it for Asian markets.

Who it doesn't suit: anyone hoping to build steady income from this category; anyone who only does English and plans to compete in the US store against Last Time Tracker and 30+ new competitors; anyone unwilling to update weekly or to promote themselves on social platforms.

How to do it: learn the playbook, not this app. Pick a small scenario that Apple and Google don't natively cover but that everyone needs (the common trait of this type of tool is "the system's built-in option works, but it's clunky"). Make it clean, with no accounts, as a one-time purchase. Have native speakers review the Traditional Chinese, Japanese, and Korean, and write store titles using the words locals would actually search (this app added "家事·保養紀錄" in its Taiwan listing). Ship a version every week with clear release notes, since those are what editors read. At launch, set a low price ($2.99 tier) to climb the paid charts, then raise it once you've earned recommendations and your ranking is stable. Remember to check whether Family Sharing should be enabled.

How to get users: Apple editorial recommendations are the main source. Taiwan, Hong Kong, and Japan are easier to get than the US store. After launch, submit through the recommendation request form in App Store Connect and clearly describe what you localized. The paid productivity charts in small storefronts have a very low threshold, and a few purchases can put you in the top 10, and being charted is itself exposure. The developer posts on Threads (many Korean and Taiwanese users are there), sharing daily development, chart screenshots, and turning bad reviews into "updates made for you". But don't expect it to bring in volume on its own. This developer has 400 followers and keeps asking whether exposure is dead.

When to move: this playbook has no clear window, but competitors increase every month, and more people are doing good Asian-language localization. The earlier you claim the localized name for a small scenario, the better.

Signs you've read it wrong: ① After the When'd I recommendation ends, it stays in the top 5 of the Taiwan paid productivity chart for a long time and its rating count climbs into the dozens or hundreds. That would mean it isn't just relying on recommendations and the product is spreading on its own, and in that case this category is worth more than C. ② Conversely, if within the next month you find several competitors that also did thorough Traditional Chinese, Japanese, and Korean work and also received Taiwan recommendations, that means many people are already on this path and editorial recommendations will get harder and harder to win.

Data and sources

• Charts, ratings, pricing: App Store charts and store pages across regions, 2026-10-28 to 11-06; Google Play store page, 11-06.
• Early timeline, recommendation history, daily download estimates: the app's page on AppInsider (appinsider.io/apps/when-d-i-6801866888).
• Developer posts: Threads @when.did.i and @when.did.i.en, check 11-06.
• Reviews: public reviews in the App Store Taiwan and Korea storefronts.
• Revenue is inferred from chart position and unit price, not verified.