July 15th 2020 - The latest version is 1.11. If you've installed Copper and aren't sure what version you have, type 'ver' or 'version_copper' at the console during gameplay to centerprint this information. This update is not backwards compatible with previous demos and saves.
Everything you need to play Copper is in the zip, but a 7+2 level episode of maps called Underdark Overbright has been created by Lunaran and Scampie to accompany it:
UDOB required updating for compatibility with 1.1, so if you wish to replay them in the future, please be sure to redownload the episode and overwrite all old files on extraction.
Copper works with any version of Quake (even the original executable), but UDOB requires an engine with support for increased limits and alpha cutout textures. Fitzquake-derived engines such as Quakespasm or MarkV are recommended. DarkPlaces is not officially supported.
Unzip the contents of the zip file into your /quake/ directory, so that the /copper/ folder is alongside, not in, the /id1/ folder.
Start your favorite Quake engine port with '-game copper' appended to the command line. Play with GL_NEAREST texture filtering, like the dark elders intended.
Running the game with a different -game prefix, or none, and changing the mod to Copper via the console in such engines that support this may lead to unwanted config state being carried over from other mods, leading to potentially unpredictable results. Bite the bullet and make a new shortcut. (Especially before reporting bugs.)
Start a new game and play through the included new episode, any (or all!) of the original episodes, or try out any custom Quake single player map that doesn't require another mod. Retry old favorites!
Here are links to download a handful of custom maps which have been found to be particularly fun with Copper, or to benefit especially from one of its features. (Thanks as always to spirit and Quaddicted for Quake archival.)