The detailed ChangeLog can be found at: http://source.otrs.org/viewvc.cgi/otrs/CHANGES?revision=1.2135&view=markup.
openSUSE / SLES
Fedora / RHEL 4,5,6 / CentOS 4,5,6
Windows installer (otrs4win), contains Apache, Perl, MySQL and OTRS
Source Archive - tar.gz
OTRS Group, the source code owner, provides world-wide enterprise support, consulting and engineering including process design, implementation, customization, application support, and fully managed service.