Basically, what it says on the tin; I need a JTA implementation useable in a J2SE application, ideally one that doesn't carry too much of a framework burden with it.
I recommend Bitronix. Before using any other transaction manager, I recommend thorough testing. Tests like killing power to various machines during each phase of the transaction. You want transactionality to protect you when failures occur. It is surprising how many transaction managers have failed to correctly implement recovery.
Bitronix does need JNDI, which is typically provided for you in a JEE container, but they include a simple embedded implementation that will support Bitronix in a JSE application.
From its webpage:
"With over 20 years of expertise in the area of transaction processing, JBoss Transactions (JBossTS) is the premier open source transaction manager.
It can be deployed within a range of application servers, containers or run stand-alone. Over the past 20 years it has been used extensively within industry and to drive standards including the OMG and Web Services."
Quote from http://jotm.ow2.org/
JOTM is an open source Transaction Manager implemented in Java. It supports several transaction models and specifications providing transaction support for clients using a wide range of middleware platforms (J2EE, CORBA, Web Services, OSGi). JOTM is hosted by the OW2 consortium. The license used by JOTM is BSD-style License. This implementation is fully functional and mature since it has been used for several years in the JOnAS application server project.