Gspace is a Firefox extension that takes the small pile of gigabytes that the Google folks give you for your Gmail account and turns them into a drive with storage and music-playing capabilities.
Accessible via a toolbar button or from the menu bar, the extension opens a new tab with an FTP-style interface. You can transfer files by highlighting them and hitting the directional arrow. Drag and drop is not available, but the plug-in is still replete with goodies. Uploading a file sends an e-mail with it attached to your Gmail. By creating an appropriate filter and folder, it can be quite easy to keep track of the files you've uploaded. Deleting the file from Gspace deletes the e-mail.
Gspace also allows users to switch between different Gmail accounts, has an Inbox button so you can quickly jump back to the standard Gmail interface, and supports different uses of the virtual drive. These include a Music mode, which can be used with a Flash music player to create a Web-based MP3 player, and a Photo mode, which can be used for displaying photos--although it didn't work for us.
Additional features include help buttons and a status bar that tells you which account you're using and the amount of space used. Gspace also can show you files uploaded with GMail Drive, a similar program, although those files aren't accessible from Gspace. Highly recommended.
Gmail Space is an extension to the Firefox browser which turns your Gmail account into a Web drive, so you can share your content from several systems without the need of carrying them with you and through a simple to use interface.