There's a form of faux-garbage-collection: you can wrap any form in `free!` and the heap pointer will be reset when that form finishes: http://microscheme.org/documentation#memman

This would be awful for general-purpose programming, but on a device with only 2.5kb of RAM to begin with you can usually pre-allocate anything that needs to survive that reset. I use this in my keyboard firmware's outer loop: http://atreus.technomancy.us/firmware2