Web2py is still pretty active, and it can now be used with Python3. Running existing applications on Python3 might require some changes, especially where 'print' is used, but staying with Python2 should just work. What version were you last using?
Py4web is a new framework for Python3 based on the lessons of web2py, with a change in how you install, how you develop views, and with a more streamlined approach to forms. The way models are loaded has been changed, and that's part of big speed-up. It is probably easier to develop new apps for it than to port web2py apps, but I haven't been out on the bleeding edge yet, so my ability to guide others is limited. There are several pioneers, though, so if you're interested keep reading the list.
/dps