FinTS 3.0 is actually a remaining of HBCI 2.2, and is meant to be the successor of HBCI that way. The technical details do not deviate that much, so that it can be expected that HBCI open source implementations will integrate FinTS in the future.
For the best discussion about this that I found so far, see this: http://www.ruby-forum.com/topic/177210
There seems to be only two (or two major) open source HBCI implementations: HBCI4Java and AqBanking. Of these two, AqBanking seems to be the preferrable one (yet without respect to Ruby integration). Reasons:
- AqBanking is behind several major HBCI open source applications: AqFinance, QBankManager, GnuCash, KMyMoney, AqBanking-CLI (source), while HBCI4Java is behind Hibiscus (source).
- AqBanking is in active development as of 2010-08, while HBCI4Java’s latest version is from mid 2009. (As of 2010-08.)
- AqBanking offers HBCI, OFX and PayPal in the open source version, while HBCI4Java offers HBCI (source).
- Both are cross-platform compatible for Linux, Mac OS X and Windows.
- AqBanking is twice as popular as HBCI4Java (40,000 vs. 18,000 Google search results).
Also, the integration into Ruby is simpler. One can either use exec() with the command line client coming with AqBanking as the simplest solution, or use the Ruby C bindings with the AqBanking library, which is written in C (see here). With HBCI4Java, one could either use Ruby Java bindings (like they do in the POI project), port the application to JRuby, or use the GUI tool Hibiscus and XML-RPC (example), which is however quite clumsy when it should be used on a server (as it’s a GUI tool).
Result: I recommend to use AqBanking with CLI based or Ruby extension based integration.