A package for classifying, partitioning and studying block designs in GAP 4.3 by Leonard H. Soicher. Free download in .tar.gz format, documentation in PDF.

A program to construct t-designs with prescribed automorphism group. C++ source code free to download, with GAP interface.

A general-purpose program for experimental designs, by N. J. A. Sloane and R.H. Hardin. Free download of beta-test C source files.