From Kolab Wiki
Aethera is compatible with the Kolab 1 format.
The free software Aethera client is available for Windows, Mac OS X and Linux.
For downloading and installation instructions, see http://www.thekompany.com/projects/aethera/download.php3 and http://sourceforge.net/projects/aethera/files/Aethera/1.2.1/
From the Aethera Home Page
"Aethera is a new cutting edge communications and personal data management software written with Qt and deployed for Linux, Windows and Macintosh. By PIM we mean Personal Information Manager, by PDR we mean Personal Data Repository, the rest should be obvious.
Aethera supports all the standard messaging protocols such as POP and IMAP with full synchronization capability as well as support for multiple identities. All the features you would expect to find in an industrial strength email system are part of Aethera. In addition there is a personal calendar and schedule, as well as "sticky" notes, "To Do" lists, an address book, groupware compatibility via Kolab, and optional plug ins the extend the idea of collaboration beyond the bounds of typical groupware with instant messaging, whiteboarding and voice over IP (VoIP). The combination of Aethera with Kolab provides you with a very powerful combination that can realistically replace Outlook/Exchange and in some cases Lotus Notes, for only the price of the hardware to install it on. There are no per server costs or per user costs unless you want the optional plug ins, which are all priced at trivial amounts. Since Aethera runs on virtually any operating system you are likely to use, it doesn't require that you make any changes on the desktop.
The Groupware portion of Aethera can be as simple as sharing your personal schedule to arrange meetings and discover scheduling conflicts, sharing your contacts or even your ideas using notes and images. There is support for Kolab Groupware server, a good solution for people who need synchronization and instant access to information. Aethera is also a GPL, this means you get the source code with the application to do whatever you want. We don't charge for Aethera, however we do have the optional plug ins that we charge for, but you are free to create your own plug ins for your own use or to give away to other people and companies.
We are available to build plug ins or add functionality on a time and materials basis if you wish to have specific customizations in a timely fashion, just contact us at . Aethera uses advanced functionality that we developed that allows you to add new plug ins with relative ease across operating systems, making Aethera truly unique and extensible. Our use of Qt from Trolltech gives us the ability to easily make the user interface multi-platform, and we take care of the rest.
Aethera is well suited, and designed, around the idea of collaboration and information management."