What is this software "Novell groupwise"

Actually, the "usually you will have a NetWare server" part is no longer true.  Besides Notes/Domino, GroupWise is the only platform-agnostic email/collaboration/messaging system.  Exchange only runs on Windows, but GroupWise server agents can run on NetWare/OES, Windows and Linux.  You don't have to have NetWare or OES to run GroupWise - it can be in an all-Windows environment if you really want to - or an all-Linux environment.

Starting with GroupWise 6 you could run GroupWise on a Windows NT server, but had to have NetWare in the mix. GroupWise 6.5 added the ability to run GroupWise on Windows without needing to have NetWare - just eDirectory. The current version, GroupWise 7 SP2, can run on NetWare/OES, Windows 2000/2003, or Linux, but still needs to have eDirectory.  Starting with the next planned release, GroupWise 8, you can even run it using "native Directory Service" integration - and I wouldn't be surprised if, in addition to eDirectory and Active Directory, you could also run it using plain-old OpenLDAP (that last is just a guess on my part...)  Yes, they're removing the requirement for eDirectory, and are making it "directory agnostic" in addition to being "platform agnostic."

For more information, go to "the horse's mouth" - http://www.novell.com/products/groupwise/

With the current GroupWise, GroupWise 7 SP2, even though you can run the server processes on Windows or on Linux (in addition to running it on NetWare/OES) you do need to install eDirectory to manage it. That's not really a drawback, because eDirectory is hands-down a billion times better than AD.  You don't need NetWare or OES.  In fact, you don't need Windows servers OR NetWare servers - when you buy GroupWise 7, it ships with eDirectory and SuSE Linux Enterprise Server - an all-inclusive package.  

Also, unlike Exchange, there are more client platforms supported by GroupWise.  Exchange has Outlook for Windows and Entourage for Mac OSX, but does not have a Linux or *nix client.  GroupWise has clients for Windows, Mac and Linux.

It's not lacking in mobile support, either.  They're constantly improving it, but GroupWise Mobile Server is available now (at no extra license cost) to provide "push" messaging to smartphones and PDA's, and there's a Blackberry Enterprise Server for GroupWise, just like there is for Exchange, to support the RIM network and Blackberry devices.  No need to go to Exchange 2007 to have mobile device "push."

GroupWise is much cheaper to buy and cheaper to keep.  With GroupWise, *all* you buy is user licensing.  You need one license for each active user.  The server components are included, and scale to much higher capacity than Exchange, with much faster and more efficient message processing.  With Microsoft Exchange, if your needs exceed the limitations of Exchange Standard, you have to get Exchange Enterprise, at a premium price, in addition to the Exchange CAL and Windows server CAL (or "Core" CAL) you have to buy for each user/mailbox.  There is no "GroupWise Enterprise" higer-priced licensing, because GroupWise is Enterprise-class from square one, straight from the box.  It's easier to manage, and has less downtime, and is far less vulnerable to exploits.  In the past 4 years, GroupWise has had fewer "critical vulnerabilities" than Exchange had in the first 6 months of 2007 alone.

You can split up the server components to as many physical servers as you want, to design the most secure, scalable and accessible solution available today.