Hamster (here)is a time tracking application that is now part of GNOME proper.
Ideally, one would be able to context-click an action in GTG, and cause that to trigger a "begin work" in Hamster.
Tasks can map directly, as they are literally what you are working on. Tags (maybe a specialized syntax) could map to Hamster's Categories. This would be ideal for keeping GTD style Contexts.