The NCBI (National Center for Biotechnology Information) development toolkit,
containing various libraries needed by NCBI applications, as well as a
software suite containing, amongst other things, NCBI BLAST 2.0.

From the README:

  The NCBI Software Development Toolkit was developed for the production and
  distribution of GenBank, Entrez, BLAST, and related services by NCBI. We
  make it freely available to the public without restriction to facilitate
  the use of NCBI by the scientific community. However, please understand
  that while we feel we have done a high quality job, this is not commercial
  software.

  The documentation lags considerably behind the software and we must make
  any changes required by our data production needs. Nontheless, many people
  have found it a useful and stable basis for a number of tools and
  applications.

WWW: http://www.ncbi.nlm.nih.gov/IEB/ToolBox/MainPage/index.html