Most posix based platforms may work more or less.
Linux - complete, all components have interfaces for linux systems.
These aren't currently supported at the moment simply because they're not getting testing, though the infrastructure is in place.
MacOsX - mostly posix, so mostly functional - only missing support for real-time timers and sockets.
Win32 - at this stage only very elementary support in ecl_config, ecl_errors, ecl_time and ecl_threads (not really usable!).
Build Time Requirements
RoS - uses the core ros stack that provides the build tools and environment for compilation.
Eigen is used by the higher level components.
Run Time Requirements
Only the minimal c/c++ libraries. On linux and macosx this usually means glibc/libstdc++. It has not yet been tested with other c/c++ libraries such as ulibc (curious though). If posix real-time support is available, it will automatically utilise that, but will fallback gracefully if it does not.