The following are recent releases, with links to the Release Notes. This allows you to easily review all changes if you are upgrading over multiple versions.

Version Release Date Supported Servers   Release Notes
3.1.3 November 2016 GS64 3.3.x and 3.2.x, and 32-bit GemStone/S   Release Notes  pdf  html
3.1.2 February 2016 GS64 3.3.x   Release Notes  pdf  html
3.1.1 April 2014 GS64 3.2.x   Release Notes
3.1 February 2012 GS64 v2.x, 3.0.x, and 3.1.x   Release Notes
3.0.1 June 2011 GS64 3.0.x and 3.1.x   Release Notes
3.0 September 2010 GS64 2.x and 32-bit GemStone/S   Release Notes