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'.
Blog
Sharing iOS development experience, ASO tips, and product design insights.
Exercise Guide for Seniors & Pregnancy: Controlling Intensity Safely with METs
For special populations, too high or too low intensity is bad. Learn how to stay in the 3-6 MET 'Golden Safety Zone' for effective and safe workouts.
Read moreThe Real Dangers of Sitting: Quantifying Sedentary Risks with MET Values
Even if you gym daily, sitting for the other 23 hours might make you an 'Active Couch Potato'. How to monitor low-MET periods to improve health?
Read moreHow to Convert METs to Calories? The Simple Formula and Calculator Guide
Want to know your exact calorie burn? Master this simple MET conversion formula, often more accurate than treadmill displays. MET Goals App does it automatically.
Read moreRunning vs Cycling vs Yoga: The Ultimate MET Value Comparison Guide
1 hour of exercise, vastly different results? Compare MET values of common sports and learn to choose your workout smarter.
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 51 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