In the wake of the glorious Guile 2.0 release, I've been working on a prototype re-implementation of GIMP's Script-Fu plugin system that uses Guile in lieu of their embedded TinyScheme. I actually got reasonably far, but then the onboard video on my beloved ZaReason UltraLap SR straight up died, so I had to sideline that project while I waited for a replacement (in the form of a new ZaReason Terra HD) to arrive.
Although I'd temporarily lost access to my GIMP patches, I did have comfortably obsolete desktop machine available to me to use to satisfy my constant, ravening need to write programs all the time. I decided that doing an R6RS Scheme implementation of Google Protocol Buffers would make a cool, discrete project: I use and enjoy protobufs at my day job, and I had a hunch that their requirements would map nicely onto the features provided by R6RS records and enumerations. It turns out I was right about that, although I've now sunk a bit more time than I was expecting into the project. But I did just manage to get an initial import of some working libraries uploaded to Google Code. Check it out here.