If you're looking to transition from Windows to Linux but your users are not technically inclined you may want to evaluate Linux XP Desktop 2008. Linux XP tries to emulate the look and feel of Microsoft Windows. The goal being to make the transition to Linux easier for those used to Microsoft like operating systems.

Cfengine is an open source tool that allows system administrators to maintain 1 to thousands of unix based systems. It automates almost every aspect of system administration. Cfengine is a direct competitor to commercial software from Blade Logic and OPsware. Both of these commercial packages come with fancy GUIs and nice features, but they also come with hefty licensing fees (can get close to $1K per server managed + maintenance fees).