One of the things that I miss coming to Mac from the Linux world is the ability to have virtual desktops. Sure, the built in Expose features are pretty slick and do a lot to help you out when working in an environment with multiple desktops but there really is just no substitute for having spare desktops avaliable at the click of a button. Enter Desktop Manager, this package is a pretty decent setup that allows you to do multiple desktops in OS X but it appears to be orphaned and pretty old.
For a while Desktop Manager was pretty nice but lacking in a few key areas (no way to move apps from one desktop to another for one). That is when I found VirtueDesktop which is a dream come true. It is not really a fork of Desktop Manager but rather a re-write. Overall the features it has are excellent, I miss not being able to drag and drop applications between desktops like I could in e17 under Linux but I can live without that.
Note that VirtueDesktop is still in beta and crashes often enough but is still well worth using. Check it out if your a Mac users that wishes for virtual desktops!