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.
R90 Sleep Method Guide: How 90-Minute Cycles Help You Sleep Better
Still feel tired after 8 hours of sleep? The R90 sleep cycle method explains why when you wake up matters more than how long you sleep. Complete guide to R90 sleep cycles, calculation methods, and common myths.
Read more2026 Open Source AI Agent Showdown: OpenClaw vs Hermes, Which Deserves Your Investment?
2026's open-source AI agent landscape: Hermes, OpenClaw, Claude Code, Codex. Which fits your workflow? Plus SkillHub skill pairing guide.
Read moreHermes Agent 2026: Why Skills Are the Ultimate Competitive Edge for AI Agents
Hermes Agent is 2026's hottest open-source AI agent. Its secret isn't the model — it's the Skills system. Make Hermes smarter over time starting with SkillHub.
Read more2026 Pet Economy Boom: How Freelance Pet Sitters Can Earn $4,000/Month
US pet industry spending will surpass $165B in 2026. 95 million households own pets, yet professional sitters remain in short supply. Here's how regular people can capitalize on this trend.
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