A Tetris clone, breakout clone, or text editor seem like something a ton of people do. A little calculator that parses and evaluates mathematical expressions.

A Tetris clone, breakout clone, or text editor seem like something a ton of people do. A little calculator that parses and evaluates mathematical expressions. An esoteric programming language implementation. A program that outputs "you are c00l" in a loop. A key/value store. A Hacker News reader app for iOS. A p2p file sharing system. An IRC client. Web forum software. A chess engine. Some Markdown-like HTML generator. A static website generator. Planetary orbit simulator. Cellular automata simulator.