I suggest SymaCas (Symbolic Manipulator Computer Algebra System). It seems to be a relatively unique name that would search well. It derives somewhat from the original project name without being so similar as to cause confusion. It is reasonably descriptive of what the program does.
Sourceforge.org and freshmeat.net searches come up clean.
Inside the software world, I'd guess the closest trademark is Symantic, and I think that is sufficiently different. A quick check of http://www.symantec.com/about/profile/policies/trademarks/currentlist.jsp shows that they don't use the "Syma" prefix on products, but always the entire name. So SymaCas shouldn't be confused for something in their product line.
Other capitalizations could be symaCAS (although in documentation that's a bit strange at the beginning of sentences), SymaCAS, or Symacas. Personally, I think I prefer SymaCas or SymaCAS as the most obviouly descriptive.
Don