I've mentioned a few times about work we did almost 10 years ago on transactional REST services. This was when JBossTS was part of the HP Netaction suite, we were working on BTP, as well as the precursor to WS-TX/WS-CAF and the world's first Web Services transactions product HP-WST.
Without reminiscing too much, in those days I was participating in the W3C Web Services Architecture working group and the topic of REST came up there quite regularly. So we decided to give it a try as far as transactions were concerned and 'hey presto' RESTful transactions were born. This was way before JAX-RS so we were hand crafting the interactions ourselves, but we demonstrated it could work with the involvement of several companies. And there is remained once HP divested themselves of their middleware division.
But having transactional REST-based services has been a pet project for a long time, so it was bound to rear its head. Especially as some people (rightly) push the Web as an integration platform (shouldn't really be news to people since the WWW has always been about integrating data). Of course there are those who say you don't need transactions in the Web or can (somehow) program around them, but they miss the point. It's a bit like saying you don't need an airbag in your car but can use a pillow (and quick reflexes) yourself to save money. Yes, transactions aren't right for all situations and some bespoke approaches may be more efficient, but if you think about what you get from a transaction system and what you'd have to do in order to obtain the same guarantees, it's more often than not worth using them.
So we originally created a student project to dust off the old REST transactions protocol(s) and implement them today. This started life before JAX-RS (again) but by the time something really happened JAX-RS (and RESTeasy) was around. Michael from the JBossTS team took this work on and did a great job. It's not finished (only the atomic outcome protocol has been implemented so far, for example). Plus the protocols haven't been changed at all since they were created back in 2000/2001. So there are still some things we need to look at and more interesting work ahead.
Is this something you should be looking at for your projects? Should you believe those people who say transactions and REST don't go together? Well as I'm fond of saying "One size does not fit all." Transactions have played a critical part in all distributed systems for over four decades and for very good reasons. Of course we have XTS and Web Services Transactions support if you're using SOAP. But maybe SOAP isn't "your thing" and HTTP is all you can use. Well in that case take a look at this. In just the same way that you wouldn't want to be using a tank in the ocean and a submarine on land, use the right software tool for the right job!