Forth is the ideal language for bootstrapping a cobbled-together computer from whatever scraps you can find. Forth gives you a shell, an assembler, a disassembler, and a rich, extensible programming language in a few kilobytes. You can peek or poke hardware interactively, or use the REPL as a calculator. Forth-style assemblers also make cross-compilation very practical.

If I was tasked with bootstrapping a post-apocalyptic computer from junk, a hard copy of a well-commented Forth implementation would be a welcome assistance.