I’ve created an app that uses clustering techniques to group emails. This is not broad groupings like Social, Updates,… that Gmail does but at a more granular level (basically message threading).
Instead of just threading emails by a Conversation or by an exact Subject match that most emails clients (incl Gmail) do, the app looks for ‘similar’ / ‘related’ emails and groups (threads) them together.
It uses various attributes on emails such as keywords, sender, time,… and finds clusters. A message may be part of two different clusters or could change cluster membership depending on a better match found.
This has the effect of compacting the Inbox for viewing. Also, clusters can be acted upon as a single entity letting you move, delete, archive entire clusters.
All of this clustering logic happens on the device, there is no server component.
App Page: http://PiEnvelope.com
App Store: http://bitly.com/envelope-itunes