combine is free software, which allows a user to make matches between files, and as a result to make file joins.
Additional features include hierarchy handling, a Guile module adapted from the Emacs calendar for performing date arithmetic, and outer joins on either or both sides of a match.
Version 0.3.3 is the first GNU version, and has a few compatibility enhancements.
Guile is a pretty strong dependency, for all the extensibility functions. The program does seem to build fine without Guile, although some features are not available.
combine is known to have compiled successfully on GNU/Linux, Mac OS X, and HP-UX systems. An early version came close on an AIX system, but I lost touch with that user. Please let me know if you have success or problems in building it.