Due to other commitments, mainly my work on FullCalendar, I will no longer be able to play as active a role in XDate’s development. I will still maintain the project for bugfixes, but I will no longer be developing new functionality.
MomentJS has since become very popular. It uses a completely different syntax than XDate or the native Date, one that is very terse and jQuery-like. Its adoption has become widespread enough where I will likely integrate it into FullCalendar instead of XDate. Not to mention that it is extremely well tested and documented.
XDate is still an important project however. It is powerful while still conforming to the familiar native Date API that many many developers already understand. If you are a user of XDate and would like to be part of its future development, please contact me.