Do any of these have python interfaces?
Also, there are other kinds of interesting solvers. For constraint problems, one can check minizinc [2]. A bit like SMT-LIB, it's a language to describe constraint problems that is supported by many solvers. It's commonly used with gecode [3]. For many problems using minizinc will be much easier than trying to convert the problem in SAT (or even SMT) format.
Happy hacking, it's a fascinating domain!
[1] http://smtlib.cs.uiowa.edu/ [2] http://www.minizinc.org/ [3] http://www.gecode.org/
We are always glad to get more feedback!
Re the licensing, pySMT is open-source and distributed under APACHE 2.0 .