The Challenge has ended, though there are a few less finished maps than expected.
You may access and vote on maps here: Here
If you think you may enter but are unsure, I urge you to do it anyways. Some people might not think they can finish in time, but they can still try.
You may get noticed for even a partial map.
Are you planning to upload some content to Quadropolis - Great! Read on!
The Cube Wiki article Distributing Maps contains the original text of this guide;
This deals with the specifics of Quadropolis postings.
It tries to prepare you for providing poished content to the community and avoid any unwanted tags, maybe even get you a starred content one. ;-)
For those looking to download the development version of Sauerbraten, you can find the project here on SourceForge.
This is the direct link to use if you want to check out:
Note: The SVN project version is now 1.7, and older clients may be unable to update/check-out!