Actual Budget is a super fast and privacy-focused app for managing your finances. At its heart is the well proven and much loved Envelope Budgeting methodology.
You own your data and can do whatever you want with it. Featuring multi-device sync, optional end-to-end encryption and so much more.

ERPNext is the world's top 100% open source ERP which supports manufacturing, distribution, retail, trading, services, education, non profits and healthcare.

Instantly share images, videos, PDFs, and links with people nearby. Peer2Peer and Open Source. No Setup, No Signup.

Flow diagram drawing. Makes it look hand-drawn.

Machine learning based system to mangle and play with the spelling of words.

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Trade, GDP, population, exports, etc... between different countries

Design wireframe of web-pages or apps online

FFT animations

Edit code/document with real-time collaboration.

Mathics is a free, general-purpose online computer algebra system featuring Mathematica-compatible syntax and functions. It is backed by highly extensible Python code, relying on SymPy for most mathematical tasks and, optionally, Sage for more advanced stuff.