On what systems will Backbone run?
The main targets are the free Unix-like systems, GNU/Linux and *BSD. We do not plan on including any system-specific features, so it will likely be portable to any sufficiently capable Unix-like system.
OPENSTEP once ran well on really slow systems (insert numbers here). We don't expect Backbone to run on systems like that. However, we do want to keep things efficient. It is our goal that Backbone be usable (but perhaps not snappy) on a high-end Pentium (~200MHz) system with 64Mb of memory.
Our display system is a DPS-like system, and is independent of the graphics system running beneath it. At first, we plan on making Backbone run on X, with the ability to use legacy X programs at the same time, but support for eg. DirectFB is certainly possible (and not entirely unlikely).