This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
There are many implementations of the JAX-RS standard. Apart from Jersey, there is also Apache CXF and JBoss RESTeasy. Perhaps there are additional frameworks that now escapes my mind.
As far as I recall, the Restlets framework also implements JAX-RS.
Note that each framework also provide more or less additional functionality outside of the specification.