Hitch — github.com/polydawn/hitch — manages a filesystem database of Releases.

Hitch is used by Layer 3 Planners (like Heft, for example) as a source of information for which Wares might be used. WareIDs discovered by scanning or produced as results of executing a Formula can be added to new releases... as can entire sets of multi-step build instructions in Layer 2 format.