I have an old 700 Mhz Pentium III at home running Windows 2000 Server, with a home router set up to pass incoming requests to it and a DynDNS account set up so it's easy to find.

Right now I'm using it for a number of things:

• Shared folders + backup inside the home network
• Shared Printer inside the home network
• Domain Controller, just because I feel like it and because it's useful to me as practice to keep those "enterprise" administration skills.
• Web Server
• FTP remote access for my files. I abandoned this for security reasons, but it's still worth leaving visible.
• Remote Desktop in to the home network (thinking about adding VPN service)
• SVN repository
• MySQL - Will be moving to SQL Server 2008 Standard soon.
• After I upgrade my wife's laptop from home to pro later this year it will also become a domain controller
• It's the only place I still have access to Internet Explorer 6 any more without setting up a new virtual machine, so I use it for testing code with that browser.

The question is: What else could I be doing with this machine?

Update
Additional ideas based on the suggestions:

• Media Server/DVR
• Build server
• PBX
• SSH
• Proxy Server
• Continuous Integration Server
• Personal OpenID Provider

Update2
Just a note that this server was recently upgraded to an Atom330 with 2 GB ram and bigger hard drive. For all that's slow for a "modern" cpu, it should still be much faster than the old Pentium III and the expected power savings should make the upgrade essentially free over the course of the next year or two. Also, it's now running Windows Server 2008.