Mobile App Development for Productivity & Health
Portfolio of independent developer Yang Sun, featuring Handwriting Book, PrivAI, Life Cabinet and more.
Featured Applications
Each app is carefully designed to improve your quality of life
QuickNotes Flashcards Watch
Effortless Exam Prep and Study
A flashcard note app designed for exam review and knowledge accumulation, supporting seamless sync between iPhone and Apple Watch.
PrivAI LLM - Local AI Chat
Local Offline LLM AI Chat
An intelligent application based on DeepSeek-R1 distilled models, designed for users who value privacy, convenience, and versatility.
Life Cabinet
Manage Your Life Blueprint by Departments
A comprehensive life planning and growth management tool that coordinates health, finance, career, learning and other aspects through departmental management.
Copybook
Handwriting Focus & Calm
A digital space for mindfulness through handwriting, helping you regain focus and calm.
R90 Sleep Assistant
Manage Your Sleep Cycle
Based on the R90 sleep method, helping you plan sleep by cycles, eliminate sleep anxiety, and regain energy.
Self-Love Project
Stop Self-Hate, Start Self-Love
Stop hating yourself into improvement. Use 'Identity Switching' rituals and a 21-day challenge to become your better self with love.
GeoFlow
Geo Arbitrage & Budget
Turn the world into your wallet. Multi-currency budgeting and geo-arbitrage analysis tool designed for digital nomads.
Rich Dad Finance Tracker
Build Assets, Not Just Budgets
A financial tool based on 'Rich Dad Poor Dad' principles, helping you distinguish assets from liabilities and focus on cashflow and passive income.
PetSitter Pro: Client Manager
Schedule, Invoice & Reports
Designed for independent pet sitters and dog walkers, helping you turn from 'amateur part-time' to 'industry expert'.
SkillHub: Discover AI Skills
Find & Save Pro Agent Skills
Build AI-driven businesses with 150+ ready-to-use skills. No coding, three-step setup.
Blog
Sharing iOS development experience, ASO tips, and product design insights.
How Many Days Between Two Dates? Count Workdays, Weekends and Exact Years-Months-Days
Days between two dates, workdays only, or the date 90 days from now: hand counting is always off by one. Here is how inclusive counting, month ends and weekends actually work, and a one-step way to do it on iPhone.
Read moreHow to Escape the Rat Race in a Cashflow-Style Money Game: Passive Income, Loans and Selling Assets
Cashflow-style money games come down to one line: passive income at or above monthly expenses. Which assets to buy, when to borrow, when to sell, and how the rebuilt game in Rich Dad Finance Tracker 1.4 works.
Read moreBest Presentation Timer for iPhone: A Segmented Timer on the Lock Screen and Dynamic Island (PaceTimer 2.0)
Glancing down at your phone to check the time is awkward and you still run over. PaceTimer 2.0 puts a segmented agenda timer on the Lock Screen and Dynamic Island. Free to use, with a one-time Pro upgrade.
Read moreHow Long Should You Leave a Face Mask On? Time It on iPhone and Keep a Mask Diary (Mask Diary 2.0)
Leave a sheet mask on too long and it can dry out; forget it and the session is wasted. Mask Diary 2.0 times it on the Dynamic Island and logs which mask you used and how it felt.
Read moreAbout Indie Developer Yang Sun
As an independent developer focused on mobile apps, I believe technology should serve life, making complex things simple and beautiful experiences accessible.
Since starting iOS development in 2020, I have released 55 apps covering productivity, health, learning, and more. Each app embodies my pursuit of user experience and product quality.
User Experience
Every detail carefully polished
Innovation
Following trends, exploring possibilities
Service
Listening to feedback, improving constantly