rainsday
KOI Keyboard
Five Chinese input modes, English in the same flow. Tap, glide, write by hand — with a keyboard that feels like yours.
iOS · CANTONESE-FIRST · CUSTOM THEMES
A SMALL STUDIO. AN OPEN UNIVERSE.
Build forwhat's next.
A Hong Kong studio turning curious ideas into
considered apps, websites and digital experiences.
01 — THE APPROACH
Small studio.
Heavy pull.
Small studio, heavy pull. We take rough ideas and compress them until they shine — iOS apps, web tools, automation, brand systems. Polished until they feel inevitable.
設計から実装、運用まで、一貫して。
- 01iOS apps
- 02Web experiences
- 03Automation
- 04Brand systems
02 — IN ORBIT
A few things
in our orbit.
Useful tools. Playful experiments.
Made with a point of view.
Updated September 2026
01 / 09
BCanteen
Tell Bao what you ate, in your own words. A Cantonese food journal that brings meals, portions and nutrition into one conversation.
iOS · CONVERSATIONAL FOOD LOG
山野蛙 · WildFrog
Hong Kong's 330 peaks, one trail at a time. GPS check-ins, summit certificates and a growing collection of mountain memories.
iOS · 330 PEAKS · v1.0.9
公道計算器
Keep group trips fair. Shared funds, multi-currency expenses, shopping lists and clear settlements — together in one place.
GROUP EXPENSES · MULTI-CURRENCY
香港體感
How does Hong Kong feel today? Eighteen-district heat, air quality, a live heat map and a little character for every kind of weather.
iOS · 18 DISTRICTS · v1.5
Quest 學習天地
Five subjects, one little learning world. Illustrated flashcards, focused practice and quick quizzes make room for a little progress every day.
WEB · 中文 / ENGLISH / MATH / SCIENCE / HUMANITIES
Love Contract
An early exploration of shared agreements, clear consent and making expectations visible.
iOS CONCEPT · RELATIONSHIPS
RaIN JLPT Grammar Lab
310 N3 and N2 grammar drills, plus vocabulary, listening and focused practice for the points that need another look.
WEB · N3 / N2 · 310 DRILLS
FIELD NOTES / RaIN
From information
to understanding.
to understanding.
SOURCES → FINDINGS → DECISIONS
Research & longform
CSV, chat-log and Excel analysis with a designer's output. Sources, findings and a clear next step.
ON REQUEST · RESEARCH / REPORTS
03 — TIME DILATION
Good things
take gravity.
That's where we work. Deep in the gravity well of a problem — small habits, shipping discipline, craft that compounds. One hour here is a launch out there.
- 01 — SHIP FIRST. POLISH EVERY ORBIT AFTER.
- 02 — AI IS THE STAFF. DIRECTION IS MINE.
- 03 — EVIDENCE BEATS PLANS.
- 04 — MATCH THE REFERENCE. APPROXIMATION ISN'T DESIGN.
×1.31 AND CLIMBING
04 — EVENT HORIZON
Notes from
the field.
- BCanteen: a Cantonese food journal, with image-led meal suggestions in development
- KOI: new light and dark keyboard themes, now in testing
- 公道計算器 / expenseCal 1.2.13 is live on the App Store
- 山野蛙 / WildFrog 1.0.9 is live — keep collecting those peaks
- 香港體感 1.5 is live on the App Store
- LAB 01: a real-time black hole with true gravitational lensing
- expenseCal: eight cloud functions live; 195 web + 122 rules tests green
- WildFrog 1.0 submitted to App Store review
- expenseCal iOS functional audit: submit-ready
- WildFrog: 330 collectible peak titles, honest GPS check-in
- 香港體感: feels-like formula rebuilt on apparent temperature
- codex-pet-meter v0.3.0 open-sourced on GitHub
- 香港體感 1.0 live on the App Store
- edition 04 archived
- expenseCal 1.5: net settlement and pair batches GA
- vibe code: three Claude Code skills shipped
⚠ 1.5 rs TO PHOTON SPHERE
05 — ESCAPE VELOCITY
Have something
in mind?
New commissions, partnerships, advisory. Send a brief — we reply within one business day.
hello@rainsday.com