What tools have you found useful for managing Macs that didn't come with the system? I'm interested in both CLI and GUI tools, a synopsis and a link.
If binaries aren't provided, are their any tricks to compiling it?
Lastly, can you give an indication of the licence or cost of the software?
Apple Remote Desktop. It's by far the most useful tool that's out there. You can do screen sharing, remote control, installing files and pkg remotely, doing hard- and software inventory and lot of other stuff. There are few tools that made my job so much more easier than this. If you have more than 3 macs in more than 2 rooms, get it. It's not very cheap though, with $299 for 10 client computers and $499 for unlimited clients.
And if you have to manage OS X Server, make sure to read the CLI admin guide, there is lot of valuable info in it which isn't very obvious because the differences to other *nixes.
The CLI that comes with OS X Server is pretty powerful and can do everything and more than what's provided via user interface. There isn't a tremendous amount of information on the web for managing OSX compared to windows or linux, but I found this blog to be quite helpful and a good place to start: http://managingosx.wordpress.com.
Otherwise, get MacPorts and you can get almost every mainstream unix tool out there. sudo port install X does it. It requires you have the developer tools for mac installed, but those are easily downloaded (or on your installation DVDs if they're handy) with a login to ADC.
TextWrangler, a freeware tool from Bare Bones Software, is a great text editor. It has a panel for accessing all your open files, lets you run scripts and capture output easily, change file encoding, does syntax highlighting, offers to unlock files you don't have permission to, and does everything you'd expect from a general-purpose text editor. [And no, I'm not affiliated with them.]
Of late, I've really enjoyed the fact that on the command-line, you can type:
edit /some/file
and it'll open it up the file. Better still, you can pipe to it:
ls /Applications | edit
where there is a lot of output, this is really a nicer way to go through it.
iftop does for network usage what top(1) does for CPU usage. It listens to network traffic on a named interface and displays a table of current bandwidth usage by pairs of hosts. Handy for answering the question "why is our ADSL link so slow?".
iftop is a GPL CLI tool that I wish I had on all of our machines. It was a piece of cake to compile from source. It lets you see what network connections are active and which way they are going. [You don't even seem to need to be root to use it in normal mode]. It also has a promiscuous mode that'll show all the traffic going through a hub or mirrored switch port.