This page illustrates some mods not designed for OpenArena, but for Quake 3 Arena (or for some other derivative games). Some of the features added by OpenArena probably will not be present, but the mods will be worthy anyway. Some mods could also be designed for ioquake3 or other idTech 3forks. Check a mod's page for more specific informations (features, how to install, compatibility issues). For OpenArena-specific mods, please see the "Mods" page.
You should always read "readme" files included with mods. It is also advisable to take a look the the "Troubleshooting" section below in this page and to similar sections in each mods page.
Note: some mods could have different versions, optimized for Quake 3 and for OpenArena.
Notes for who wants to write/expand the pages about mods here:
Important: when you update the pages dedicated to the mods, you can indicate if a mod has, for example, problems with missing textures or similar. If you test new versions of mods or OpenArena, please update the main list here below... but in the page dedicated to the specific mod, if there is a compatibility "table", it would be better to add a new line for the new test, instead of replacing the previous: please add (example) instead of replace (example) there.
Another important thing: when doing your tests, to be sure if there are or not "missing textures" problems, you should (at least, temporarily) remove your additional third-part Q3A-OA texture compatibility packs, if you have installed any: they could be in your baseoa folder under your installation folder and/or under your autodownloaded data folder (please read here). Please do the same with third part Q3A-OA model or map compatibility packs, if you have any. Doing this, your description will be valid for any player that uses that version of OpenArena, without third-part compatibility packs (otherwise, you may tell "no problem", where instead another player may experience many missing textures).
Technically, it is even possible to run Quake3 as a mod under OpenArena. A quick test showed that copying the "baseq3" folder (already patched to PointRelease 1.32c) under the OpenArena 0.8.5 installation folder, then launching it as a mod works, although with some errors showed up in console and some graphic textures and effects appearing strangely. Not sure if a such use would be permitted by Q3 EULA. Anyway, that would allow to take advantage of some engine improvements, but would not enable the many extra features managed by OpenArena game logic (just like using any old mod).
If you have problems, check the FAQ and Troubleshooting page, search for "readme" or "help" files inside the mods' folders, and check compatibilty notes in our pages about them here. You can also go to the forum.
If your problem is that when you start any mod from the "Mods" menù, the sound stops working at all, please check here.
Remember that OpenArena is derived from the latest patches (PointReleases) of Quake III Arena: mods written for versions too old of Q3 probably will not work here, if the two PointReleases were too different (even on Quake3: a mod written for Q3A version 1.17 probably will not work under version 1.32). In this case, try if you can find a more recent version of that mod somewhere, it should be designed for Quake3 version 1.27 or later.
Important: some mods include their own maps... in that case you may need a Q3A2OA texture compatibily pack, as mentioned in FAQ#Maps designed for Quake 3.
Please notice that OpenArena 0.8.8 added some new autoswitch weapons modes (and changed the default mode to one of these), and such additional modes are not supported by old mods, that know only "always" and "never" autoswitch modes. Please read autoswitch weapons for more infos.
In general, mods may lack some features that were not available in Quake3, and that were later added by OpenArena (e.g. some graphic options and some special game options). Some features, managed by the engine, may work if enabled via console although the graphic interface does not mention them.... other OpenArena features are managed by the gamecode (game logic) instead, and each mod usually uses its own game logic, so probably such features would not work at all in mods based upon Q3 gamecode or upon previous OA versions gamecode.