What a great list! Adding some suggestions... some I've done, others are goals (especially APL and Prolog) 1. Design a new programming language. Prove it Turi

What a great list! Adding some suggestions... some I've done, others are goals (especially APL and Prolog) 1. Design a new programming language. Prove it Turing complete (or go back to the design phase). Maybe do a compiler for it. 2. Design some hardware. There's cheap FPGAs and nice walkthroughs for architectures like the 6502, but my next project will probably be a custom architecture because I've never done a proper compiler before. 3. Raytracers! I did one in JavaScript back in '02... ah, how languages evolve... 4. Break your language paradigms! Learn Lisp, APL, Prolog, Haskell... This is a meta-challenge: do another challenging project in an unfamiliar language, and get to know powerful idioms in the language and how they're handled behind the scenes.