Is it possible to postprocess Trimble .ssf files without Trimble Pathfinder Office (differential correction - our sporadic use does not defend realtime correction subscription) ? We only need the correction utility but the pathfinder package contains a lot more and is too expensive just for this. I have not yet found open source software which supports ssf.
Unfortunately I haven't found an Open Source solution.
However, there is a Trimble extension in ArcMap called GPS Analyst that will post-process
.ssf files. They have also released a new version for ArcGIS 10.1 called Trimble Positions desktop addin that is the current ESRI solution.
I cannot answer but this other question may give you some useful material.
RTKLIB is the reference open source post-processing solution, but it doesn't seem to support .ssf (yet?).
You could use the SSF to RINEX utility included in the GPS Pathfinder Office (viewer mode requires no license). Then use RTKLIB to post-process the data. There might be issues with the RINEX file, though, see SSF to RINEX problem