The paper is undergoing its final revisions, and the referee has indicated that these will make it acceptable, so I think we're in the home stretch of getting it published. That means that I'm consolidating my code a bit in preparation for testing our algorithm on Barnes-Hut-style cosmological simulations. The PlaneT package is a result of that consolidation.
My current plan is to gin up a prototype Barnes-Hut tree code in PLT Scheme (shouldn't take long---it's really pretty easy to code). Once I've got that working, I'll start converting the important bits to C that I can link into PLT Scheme. This is for speed. The IC code currently takes about 2 minutes on my machine to generate a million-body system, while similar C code I've used takes as short as 10 seconds. There will likely be a similar factor for the integrator code.
We'll be wanting to test our integrator on large systems (i.e. around a million bodies), so coding the bottlenecks in C will be necessary. I'll be using as little of it as possible, however, because scheme is so much more pleasant.
I'm looking at this future work as a grand experiment to see whether it's practical to develop physics simulation code this way. I know that other people have done it before, but I want to see how it works for me.