You might also want to look at the Decision Procedure Toolkit (DPT): http://dpt.sourceforge.net/

DPT is an open source (Apache 2 licensed, source forge hosted) SMT solver implemented in OCaml with good performance.  The current release supports only SAT + EUF, but future releases will soon add integer and rational linear arithmetic – of course, you can always add the theory you want yourself.

Kind regards

Jim Grundy