Transactions are not considered a REST best-practice. In fact, they are a REST anti-pattern. Needless to say, some environments do have transactional requirements. Even if not purely REST, these applications should be able to take advantage of RESTful principals when interacting with a Transaction Manager.
REST-* Transactions is a specification that attempts to define a RESTful interface for 2-Phase-Commit transactions. It describes the interaction between coordinator services and transaction participants as well as how transactions can propagate in distributed applications.
Anybody is welcome to participate in the discussions to drive the specification. Modifications of or alternatives to the current draft are highly encouraged. Check out our collaboration page for more information.