Here are some compiled versions of Unison. For more information about Unison, please see the project page or the Yahoo discussion group.

Mac OS X


Text version: Use the GUI version, and do a “Unison -> Install Command line tool”
GUI Universal Binary: 2.27.72 (2008.05.29, stable. This has been tested on Leopard intel and PPC. If something goes wrong, please drop me a line), 2.30.6 (2008.07.01, experimental)

Windows


Thanks to Karl M, here are native MSVC Windows version (GTK+, at least version 2.12, and text versions in each zip file): 2.26.14, 2.27.57 (2008.01.20, stable), 2.28.34 (2008.01.20, unstable), 2.30.4 (2008.06.28, experimental)
A GTK+ 2.12 runtime environment, needed to run this version, may be downloaded from the Pidgin project.

Windows Text Only, Experimental version: 2.30.3 (2008.06.27), 2.30.6-cygwin (2008.07.01, requires the cygwin dll)

Linux


Thanks to Mike Elkevizth, here is Linux GTK+ version compile on CentOS 4.6. 2.27.57 (2008.02.04, stable)