Stacks v3.1 is a free update with lots of additions for RapidWeaver 7. Plus a few extra API features and performance improvements.
You can read more about it here on our Blog: http://blog.yourhead.com/stacks-v3-1-0/
You can download it directly from our website or RapidWeaver should auto-update to v3.1 the next time you use Stacks.
If you follow along with the beta releases, this version is identical to the final beta version yesterday.