I do not know these tools, but I found these links over time:

- Flex (from lex) implementation: https://github.com/westes/flex
- Invisible-Island, home of some of the tools you quoted: http://invisible-island.net
- yasm (from nasm): http://yasm.tortall.net
- nasm (assembler): http://www.nasm.us
- explanations and book references: http://dinosaur.compilertools.net

Maybe you already know most of them. As I do not know these tools, I can not help much more...

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If you want to have fun with a simple compiler (this one for C), you may have a look at scc development: http://git.suckless.org/scc