Venus AFAIK is not available for ti83plus/ti83plus but only for ti83 regular (or ti82stats). Venus is ION compatible so you can launch ION games with Venus. You can get it here :
http://www.ticalc.org/archives/files/fileinfo/171/17170.html
Ion is available for ti83 regular and ti83plus/ti84plus. It's a tiny shell and provides some extra useful libs (for programmers). Download ION here :
http://www.ticalc.org/archives/files/fileinfo/130/13058.html
(83g is for ti83regular and 8xp is for ti83plus/ti84plus)
MirageOS is available for ti83plus/ti84plus, it's a flashapp (it goes into APPS menu, not PRGM). It's ION compatible and could also run mirageOS games and do some extra tasks. You can download MirageOS here :
http://www.ticalc.org/archives/files/fileinfo/139/13949.html
Doorcs is the biggest and the most featured shell, it includes compatibility with other shells, a very nice graphical user interface, mouse support and more. You can download it here :
http://www.ticalc.org/archives/files/fileinfo/430/43068.html
More information about doorcs (currently 7.1) here :
http://dcs.cemetech.net/index.php/Main_Page
