There are 3 newer versions of Workbench/AmigaOS since 3.1. These are: AmigaOS3.5, AmigaOS3.9 and now finally AmigaOS4.0.
The 4.0 is still not completly finished but exist in a pre release beta stage and 4.0 will only run on Amigas equipped with ppc accelrator or the newer AmigaONE. It currently runs only on the AmigaONE.
OS3.5 and 3.9 works on the classic amiga as long as you have enough ram and kickstart 3.1.
Here are a link to info about os3.9
http://www.amigau.com/aig/amigaos39.htmland os4 here:
http://os4.hyperion-entertainment.biz/
