I didn't know about ypsilon! The incremental/short pause GC looks very interesting indeed (although for the current usage in The Spatials I run TinyScheme as part of the map generation and then I completely unload it, so no GC, all the script logic gets encoded into command-like objets inside the C++ heap). But it appears it hasn't been developed for awhile. Still it's quite small, I will definitely look into in the future.