foma is a compiler, programming language, and C library for constructing finite-state automata and transducers for various uses. It has specific support for many natural language processing applications such as producing morphological analyzers. Although NLP applications are probably the main use of foma, it is sufficiently generic to use for a large number of purposes. It comes with an xfst-compatible interface and regular expression language. The library contains efficient implementations of all classical automata/transducer algorithms: determinization, minimization, epsilon-removal, composition, and boolean operations. More advanced construction methods are also available: context restriction, quotients, first-order regular logic, transducers from replacement rules, etc.
ACOPOST is a set of freely available POS taggers modeled after well-known techniques. The programs are written in C (aiming for extreme portability and code correctness/safety) and run under various Unix flavors (and probably even under Windows). ACOPOST currently consists of four taggers that are based on different frameworks: Maximum Entropy Tagger (MET), Trigram Tagger (T3, based on Hidden Markov Models), Error-driven Transformation-based Tagger (TBT or Brill Tagger), and Example-based tagger (ET).