I'm not a developer or major community wrangler or anything, but the way the various projects look to me...

• "Maemo" is/was Nokia's Internet Tablets OS based on Debian, using the GTK Hildon framework plus ever-increasing amounts of Qt.
• "Moblin" is/was Intel and the Linux Foundation's OS based more or less on Mandriva, using a GTK framework of some kind.
• "MeeGo" is a failed merger attempt between Maemo and Moblin - Mandriva base plus Qt framework. It has also been used as the name of Maemo version 6, which wholeheartedly embraced Qt.
• "Tizen" is essentially Intel/LF's successor to Moblin, with a few Maemo folks involved, using HTML5 As A Software Framework and EFL. (Incidentally, that last leaves me screaming in horror.)
• "Mer" WAS originally a community update project (Hildon-based) that was to be a successor to Maemo. It is now a project based on the Maemo/Moblin merger attempt (Qt-based) which may end up hooking up with Tizen but hasn't officially done so yet.
• "Meltemi" is Nokia's next Linux OS which may or may not be a successor to Maemo and/or an Android competitor and/or the fifth horseman of the apocalypse and/or something else entirely. Rumor suggests it'll use Qt, but for all we know for sure it could be using OpenMotif or something.

Does that help?