No work has been done on Tapestry 4. There is a backlog of issues in JIRA but nobody has stepped forward to work on them.
A series of release candidates were voted up. 5.0.16 and 5.0.17 had minor issues that were corrected for 5.0.18, which was subsequently voted as the final release for 5.0.
A set of performance improvements for Tapestry 5.0 are in the 5.0 branch; if released this will be 5.0.19. However, the same changes are available in 5.1.
A significant number of new features have been added to Tapestry 5.1. We are hoping to have a 5.1 final release available in just a few months. We think it is important to the perceived stability of Tapestry that a release that builds on 5.0 but stays fully compatible be made available.
New committers added to the project over the last year have continued to contribute very lightly. The vast bulk of the code continues to be developed by Howard Lewis Ship. With no committers "stepping up to the bat", there has been no progress on expanding the membership of the PMC.
That being said, the rest of the community is lively, with many users mentoring each other in the user list, a steady flow of issues (some with patches), and a respectable number of messages (79 messages / day, across the three mailing lists, according to MarkMail.org).