Cycle is a collection of modules that will eventually comprise a full product development suite.
The Hub is the central point of user information. It handles registration and authentication of users for the other parts of Cycle.
Spokes is essentially a forum software with an API to allow other parts of Cycle to read/write from. One could set up an instance of Spokes on its own (with Hub) as a stand-alone forum.
Frame is where products are described and where issues/bugs are tracked. Items in Frame are accompanied by Spokes topics for communication.
Bars is where progress on Frame items are tracked.