We had a building event on a ClassicGen server
Trailer:
http://www.youtube.com/watch?&v=QwUOgXun5v8

The Basics
You may think the graphics are sort of crappy, but it's much deeper than the graphics. You can make your own skins, scopes, even maps. Oh yeah, you can build too. It was made in 2011 by Ben Aksoy and bought by Jagex during beta. Jagex announced that on December second, they would shut down the master server. This was basically the last straw, and thus, buildandshoot was born from the efforts of izzy, Stackoverflow and danhezee.

Aloha
One of the biggest server groups is Aloha. izzy is the host of the Aloha servers, and because of him, over 20 out of the 89 AoS servers are Aloha's. Some gamemodes and servers include:
Babel - Both teams race to build towers up to a giant blue platform in the sky (the "heavens") and capture the intel.
1ctf Pinpoint - Pinpoint, a map made by izzy himself, runs 24/7 on this server. The noteworthy part of this server, is that the only intel  is in                           the very center.
Arena - In this gamemode, you have one life per round. The team that wipes out the other team completely takes the round. If no teams are               taken down, the round ends in a tie. Arena maps are significantly smaller than other maps.

Minit
Another large server group is Minit. Run by Enari and topo, they host eight servers, most of which run the Team Deathmatch gamemode. Some servers include:
Minit Classic Assault - Runs the Assault map 24/7, with squads and airstrikes, but no water damage. Green spawns on a low, flat area,                                          while blue spawns on a high tower. Inspired by the Goonhaven 2 server, which was taken down a while ago.
Minit Push - A new-ish gamemode in which teams spawn on islands on different sides of the map. The goal is to build bridges across the                       islands to capture the intel at your team's CP.

General rules
Of course, like other games, Ace of Spades has rules. General rules include no hacking, no griefing, no racism, etc.

Servers - where can I find them?
You can find the Aloha and Minit servers on their respective websites - http://aloha.pk/ and http://minit.nu
Other servers can be found on the BuildandShoot server list - http://buildandshoot.com/serverlist_page.php

How to download
To download just go to the buildandshoot website, hover your mouse over "How to Install" and click on download & install.
Other versions

0.35 and 0.58 are other versions that are available, downloadable here -
0.35
0.58 (To connect join this irc channel and ask `10se1ucgo` to put up his server, if he's there)
Extract the .zip somewhere and make sure to change your name in the config.ini

How to customize 0.75 skins - follow the steps located here: http://imgur.com/a/JAlDw
0.58 is basically the same.
WARNING: DO NOT TRY TO EDIT 0.35 SKINS OR SCOPES.