I’ve recently been sent details of SeqAn, an open source C++ library of efficient algorithms and data structures for the analysis of sequences with the focus on biological data. It is released under BSD/3-clause license and is supported under Mac OS X: GNU/g++, LLVM/Clang (3.0+).
Andreas Döring, David Weese, Tobias Rausch and Knut Reinert. SeqAn an efficient, generic C++ library for sequence analysis. BMC Bioinformatics, 9:11, 2008. DOI