JBossTS began life before Java and the concept of Application Servers. It is not tied to any specific deployment environment. Hence allthough it is the default transaction manager within JBossAS, it can be used without any additional runtime dependencies. For more details about supported platforms see the supported options.
If you are interested in deploying JBossTS into Spring, then check out the wiki.
If you are interested in running JBossTS stand-alone, then take a look at the architecture overview and pay particular attention to Transactional Objects For Java if you want to build your own transactional resources that are not tied to XA and can support nested transactions.
Remember that in all deployment configurations, JBossTS supports automatic failure recovery.