I've been spending a bit of time on a skeletal animation system. I've written the core of the bone, rig, and animation classes, so now I can animate a rig. The next step is to bind vertices so that I can animate actual models, followed by writing tools to export the data from a modelling package (or load or convert from an existing format, whichever I decide is easier).
The problem is thus; the way I planned to animate the vertices will not work because of the data format. Either I change the format with much effort and lose any hope of getting the engine to work on the PSP (admittedly a rather distant hope at this point), or I use an unpleasant and inefficient work-around. So for now I'm putting it off, hopefully I'll get the chance to do some reading and maybe I'll spot something that I'm missing.