Well, with a bit of research, I have found that OpenCraft works on all platforms.

I really have no clue on how good it is, as I have not tested it yet, but hey, anything is better than the boring Vanilla server that Notch gives us.

This custom server features the following:
custom commands (more on this later)
Multiworld (almost a requirement nowadays with minecraft servers)
Universal compatibility (works on Windows, OSX, and Linux)

The README.TXT that is given is written heavily for mac users, I am assuming that the input commands that you need to put in are the same, but if you are a Windows user or a Linux user, and my statement is false, please let me know.

EDIT: well it appears that my opencraft.zip attachment does not work, I will find a way to fix this.  For the time being,  there will be no attachment.
EDIT2: This problem has been solved. I have uploaded it to 4shared, and the URL for it is below

Download OpenCraft