combine is free software, which allows a user to make matches between files, and as a result to make file joins, aggregations, and frequency counts. combine is a part of the GNU Project.
The first version released publicly is 0.3. It appears to be relatively solid, but it lacks a bit in documentation, test cases, and validation of the consistency of options.
Version 0.3.1 included better compilation success when guile is not present or on non-GNU systems. There are also some performance improvements, emulations of the join and cut command lines, and some updates to the documentation.
Version 0.3.2 fixes a few minor things that were wrong, including summation of fractions and the missing -P option.
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.