More Gmail utilities:
http://www.marklyon.org/gmail/gmailapps.htm
Quote from the website:
I have collected links to many applications that make GMail easier to use. If you find others, please let me know at marklyon [at] gmail [dot] com.
Tim Commer's OSX Applescript
Makes using GML .4 much easier on OSX.
Trevor Harmon's mBox Cleaner
Fixes pesky mBox files created in Mozilla or Thunderbird, and good for double checking others as well. Included are both the source and the compiled version.
ReadPST
This application may be able to directly convert your Outlook PST files into mBox files GML can use. It's a command line utility, execute readpst.exe for instructions.
Outport
Exports data from Outlook to some sueful formats for upload to GMail, and other uses.
DBXConv
Can convert DBX files (from Microsoft Outlook Express) into mBox format.
gExodus
This application was designed to include some of the original features of GML but include a GUI. It only includes support for mBox files. I have since added a graphical interface to GML, and support more message store types, but this utility may be of use if GML doesn't work for you.
Pop Goes the GMail
Lets you access your GMail account with a POP3 mail client.
GmailerXP
This program, still in development, will offer total control of your GMail account from any Windows computer.
GTray
Lives in your system tray and alerts you to pending GMails.
GCount
Lives on your Mac and alerts you to pending GMails.
Mail Notifier & Address Importer
An open source .NET GMail API and a windows utiltiy that provides notification and address book import.
AddressBook to CSV 1.1
Converts OSX AddressBook format to CSV for GMail import.
GMail Notifier
For FireFox/Mozilla, adds an icon to your toolbar that keeps you updated on the number of GMails you have waiting.
G-Mailto
Rewrites any mailto link on a web page so that it sends using your GMail account and not your local mail client.
G-Mailto for Mac
Same as above, but works on computers with pretty apples on them.
GMail Compose
Adds a context menu to Firefox that lets you right click a mailto link and compose a new GMail..
G-Mailto Bookmarklet
Launch a new GMail with a bookmark!
PST Reader
Can convert PST files (from Microsoft Outlook) into mBox format.
GetMail
Auto-Forwards Hotmail messages to GMail.
YoSucker
Makes it possible to access your Yahoo! Mail using a POP3 client. Some have successfully used this application to download their Yahoo! Mail and then re-upload it with GML.
libgmail
A project to allow Python applications access to the Gmail service. Included are demonstration utilities to archive mail to mbox format, allow sending by standard mail clients via a SMTP proxy and selected download of mail attachments using a standard FTP client via a FTP proxy.
Using GMail For Backup
PHP script that can be used to backup files to Gmail and then quickly retrieve them back if and when you need them.