The versions of these that I tinker with in my spare time are a little too ambitious to reach fruition as spare-time hobby projects (especially since there's al

The versions of these that I tinker with in my spare time are a little too ambitious to reach fruition as spare-time hobby projects (especially since there's also other stuff that occupies my spare time), but I do sometimes break off bits and pieces that become either smaller hobby projects or products that make me some money. For example, some of the effort on the 3D stuff ended up in a prototype of a networked multiplayer game. I built that with a Scheme compiler, and the author of the Scheme compiler presented it at a developer conference one year as a way of showing something interesting that could be done with his compiler. I used one of the implementations of my experimental Lisp in an educational game about resource allocation for the Office of Naval Research. I wrote the rules engine, the event-handling system, and a compiler for those subsystems so that the delivered game didn't need the Lisp to run.