Nenrin – Same Day, Every Year

Nenrin (年輪, "tree rings") is a diary made of just 365 files: one Markdown file for each day of the year. Whatever you write on a given day goes into that day's file under a "## year" heading — so every year's entry for today stacks on the same page. Write today, and next year's you opens this page and reads it.

The more years you keep it, the better it gets.

TODAY
The app opens on today's page. Past years sit in a row of chips above the entry; tap one to switch, or hold the text and pull down to go back a year. Years you skipped on this day are pointed out, and you can fill them in any time.
The entry is a Markdown editor: headings, lists, quotes and bold are highlighted as you type, with a row of marks above the keyboard for quick insertion.
Photos you took on this day appear below the entry — read from your library, never written into the file.

YEAR
A heatmap of all twelve months. Each cell is one file; the darker it is, the more years that day has been written in. One ring a year, deeper each time.
Full-text search covers every year in all 365 files: search a word and watch it cross the years.

ON THIS DAY
A home-screen widget that shows what you wrote on today's date in past years.

NIGHTLY REMINDER
A nudge at the time you choose to write today's lines.

YOUR FILES, YOUR RULES
• Plain Markdown you can open in any editor
• Keep it on your iPhone (visible in the Files app) or point it at a folder in iCloud Drive
• Point Nenrin for Mac at the same folder and both write the same diary; saves replace only the current year's section, so writing on two devices never overwrites the other
• No account, no server of ours — your diary lives only on your devices and in your own iCloud Drive