Jalview is open source, and primarily written in Java. The Jalview Release History lists all of the previous versions and links to their release notes. If you want to use an earlier Jalview version, take a look at the Jalview Version Archive.
If you want to report a bug, suggest a new feature, or generally help make Jalview better, then please take a look at the Jalview JIRA bugtracker.
If you want to contribute code to Jalview, then sign up at our issue tracker, and send an email the Jalview coordinator (Jim Procter). They will then set it up so that you can be a developer on the Jalview project. If you want to add new calculation services to the Jalview desktop, then you might also be interested in working on Jalview’s sister project, JABAWS.
We are happy to help out if you want to use Jalview for your own research project. Get in contact with Jim or Geoff directly or via the Jalview Discussion Forum .