So far, no single program beats Microsoft Outlook’s combination of
e-mail features, calendaring, and contacts. But one program,
Novell’s free, open-source Evolution, comes close.
Though mostly enjoyed by Linux users as part of the Gnome window manager included with many distributions, Novell and some kind-hearted Evolution fans have created a Windows version as well. Though not an Outlook clone, Evolution offers the same general PIM landscape, including mail, contact, calendar, note, and task modules. Features include must-haves like rule-based filtering and spam detection, HTML-format messages, and PGP signing and encryption, and the ability to share calendars with others via the Web.
–Scott Spanbauer