Shattered Ascension: A redesign of Twilight Imperium 3rd Edition
Current version is 4.2 (beta), which is maintained by PsiComa here.
Shattered Ascension is a set of rules developed in order to improve balance and dynamics of Twilight Imperium 3rd Edition. These rules require the expansion set Shattered Empires to use. This version is not directly compatible with Shards of the Throne, but the usable components and required tweaks are specified in rules PDF.
There is a VASSAL extension created by marsman57 for VASSAL TI3 mod version 2.3.3, which is not available on the wiki yet, but you can download from the forum thread. The VASSAL extension is in beta, but supports the core functionality (with a few minor omissions to be fixed at a later time) to allow PBF games using current SA rules.
Shattered Ascension has been in development for more than a decade, and has been honed into it's current form over many hundreds of games by a large and diverse community. The current tools and VASSAL client support both duel (1v1) SA games and any other number of players up to 8.
Check back later.
PsiComa (author and maintainer) about rules or general questions pertaining to SA.
marsman57 (extension maintainer) about VASSAL extension related questions.
happygrue (wiki maintainer) about playing or GMing an SA PBF game, including how to get started!