I've written some: a programming language interpreter based on Abadi and Cardelli's untyped ς-calculus; a two-kilobyte web server in assembly (which accidentally did turn out to be useful); a self-compiling compiler from a sort of Forth dialect to i386 ELF executables; a translator from standard English orthography to an ASCII alphanumeric phonetic orthography I designed; a one-kilobyte programming language interpreter with dynamic multimethod dispatch and pattern-matching; a base-3 calendar based on the Sierpinski triangle; a C interpreter in Python I used for bytebeat livecoding; several implementations of Tetris, one of which is a 2K ARM executable; an operating system for ARM consisting of five instructions; a few raytracers; a Space Invaders game; a minimal roguelike in Forth; a library for manipulating Boolean functions as Zhegalkin polynomials; many symbolic differentiators; a sort of polyrhythmic drum machine called Pygmusic; a parametric CAD system in PostScript for laser-cutting MDF; 3-D rotating objects in ASCII art in 20 lines of Python; Karplus-Strong string synthesis in one line of C; an audio PLL in one line of C; an RPN calculator with forward-mode automatic differentiation; a slide rule in Tcl/Tk; a port of the logic-programming EDSL μKanren to OCaml; several fractal renderers; a decoder for the "gridfonts" Hofstadter and his research group designed; a Hershey font decoder; several maze generators; a generator for balanced-nonary multiplication tables; a vocoder; a Doom-like first-person raycaster; a teapot mod for the Minetest game; a compiler for a subset of Scheme written in itself; etc.
A lot of this is in http://canonical.org/~kragen/sw/dev3/ which you can clone with Git. I'd be happy to elaborate on any of these if you are interested.