Over the past few years there's been a backlash against application servers (both commercial and open source), with some people saying they're too heavy-weight. I'm not going to get into that argument here, but what does surprise me is the number of open source transaction managers that are trying to differentiate themselves on this very fact, as if it was something new and wonderful. Well guys I hate to break it to you but we, IBM, BEA and a few others have been doing that for years. In the open source arena, JBossTS was the first to run outside of an application server simply because it began life before there was such a thing! We've continued that over the intervening years, but maybe I just need to make it more explicit: JBossTS does not require any application server within which to run. I'm pretty sure I mentioned this before, but it's also highly embeddable, which we have proved time and again (yes, footprint size is very small, but the architecture is designed so that it doesn't require anything from the underlying environment).
Then there are some transaction service implementations (typically open source, but not exclusively) that seem to need to try to differentiate themselves by pouring scorn on transaction standards like OTS/JTS or WS-T: guys, if you have problems with these things then get involved in the process, but don't cry foul because the rest of the industry (and users) have got together to develop them. Oh, and yes while it's true that JBossTS has been at the forefront of these (and other) standards since the start, the architecture is not built on any of them since, once again, with the exception of XA they all came after JBossTS (aka Arjuna) started life.
Now maybe we don't go around "blowing our own trumpet" enough, but I think that's got a lot to do with our background: in academia there's a heavy peer review process that permeates throughout everything you do and unsubstantiated statements quickly become something you avoid like the plague. We've had 20+ years to document what we've done in this way, so everything has been verified and screened for accuracy. Maybe we assume too much that people will check that backlog of information, particularly in this day and age with so many good internet search engines. However, maybe we need to change that and start revisiting our previous publications and discussions more to refresh people's memories.
So if you're a user looking for some or all of the following: power, configurability, performance, openness, pedigree, flexibility, excellent documentation, standards (where necessary), extensibility, embeddability, stand-alone or application server deployment options, continuous vision, knowledge base, 24x7 support, etc. etc., then there really is only one option: JBossTS. TIBCO, webMethods and many others over the past 20+ years have made the JBossTS choice and found it to be the right one.