Glow is an open-source GUI calendar effort. I can’t really tell without looking around more whether it’s going after the Exchange calendaring server stuff, but honestly, that’s the part of Outlook that I appreciate most: scheduling meetings. The email part is nothing special. I dislike the archive format immensely, and the constant connection to the Exchange server to be useful is the most aggravating thing imagineable when you are working remotely, especially via dial-up (which is, of course, excruciating under any circumstances once you’ve become accustomed to broadband). Still, seems like a quixotic project to me.