Jython, or what was originally JPython, was one of the first scripting languages to be released for the JVM. Its intent was to provide a Python implementation for the Java platform. In this respect it mostly succeeds, as it implements all but a small portion of the Python language. Python itself was one of the original scripting languages (along with Perl). It has retained its popularity over the years as one of the best all-purpose languages, and it is widely used inside of Google, which employs its original developer, Guido van Rossum.
Jython has been through a succession of lead programmers; the project essentially stalled from 2005 to 2008, leading to a dissipation of the community. In the interim, other scripting languages for the JVM, notably Groovy, gained traction and Jython was never able to regain momentum.
The Jython language, however, found its way into commercial applications, and it is one of the two officially supported scripting languages in WebSphere Application Server, IBM's commercial Java EE product.
Jython initially received a warm reception, but after its principal developer, Jim Hugunin, left the project to work at Microsoft the language began to flounder. (At Microsoft Hugunin wrote IronPython, a version of Python tailored to the .Net CLR.)