Shelta is an extremely minimal Forth-like language with barely any semantics; it relies on inline machine code to write anything resembling an actual program in it. In the spirit of compilers for languages such as FALSE and brainfuck, a Shelta-to-8086 compiler was implemented (with help from Ben Olmstead) in less than 512 bytes of 80286 machine code. What's more, it's also been bootstrapped — that is to say, a Shelta compiler was written in Shelta, which was compiled with the original compiler, and then compiled again with the resulting compiler, producing a wholly self-hosted executable!
[ `Hello, _32 `world! _13 _10 ] \15 outs \0 halt