From the
web description: GmailerXP is the be-all-end-all utility app for Google's Gmail service. The program allows users to do anything that they can do online, it also combines all the features of the other programs (GML, Gmailto, etc.) The ONLY Gmail app you'll ever need. You can read more about its features
here.
To me it always sounds a bit suspicious if someone makes the "all you'll ever need" claim, but since it is going to be available for free, you should give it a try.
Note that there is no binary download available yet, but you can already download the sources from
SourceForge.