When you move to gmail or google apps you can no longer use the build in 'send to mail recipient as attachment' menu option of MS Office and other windows applications without installing a local mail client. The Right click menu of files in explorer Send To -> Mail recipient doesn't work either. Tvhgooglemapi is a simple tool that pretends to be a real mail client to windows but really only uploads the mail to the drafts folder of gmail and then opens the draft in the default webbrowser. For the user this is almost exactly the same as having the gmail web interface as the default mailclient for some windows applications (the only difference being that he has to login twice if he is not already logged in to gmail and doesn't let the tool remember the password.)