Here are two goodies all the way back from 2006. Back in B11, there was no menu option available to change maps. Grasslands was it at this point. So, users made total conversions for new maps they created and released them as hosts for any additional non-scene mods. I have saved two such total conversions, Lunar Tomato B11 and Lockdown B11. In my opinion, these are the essence of what Cortex Command used to be: single bullets were lethal, crafts and enemies piled up, gold digging was much more profitable, and there was a balanced rock-beats-scissors relationship between equipment. There is no build mode, the AI is pretty bad, and the resolution is fixed at 640x480, but this never mattered; the gameplay spoke for itself.

These are standalone versions of Build 11; as such, you need only extract to a location, open the folder, and run. The installer for build 11 can still be found on this same site (http://www.datarealms.com/downloads/ccsetup11.exe); the only way these total conversions are different are the modifications made to Base.rte. I also have put up a collection of 127 hard to find mods for Build 11. I recommend enabling all of them, and eliminating the ones you don't use. Here are descriptions of the two maps:

Lockdown: A modified version of grasslands. Has a new bunker module with all entrances "locked down," and a mining room under the rocket silo. Your brain has been placed off the map, so you can play as long as you please without worrying about it.
Lunar Tomato: A space version of popular map at the time. Low gravity means diggers work as maneuvering thrusters. The only change I have made is adding amrobotics' A-1 Molemachine to the map when it starts, since the low gravity make it impossible to order any craft that isn't vanilla.

Here's a video showing some mods in action on Lunar Tomato B11:


Downloads:
Filefront
Lockdown B11: http://www.gamefront.com/files/22730494/B11___Lockdown_rar
Lunar Tomato B11: http://www.gamefront.com/files/22730495/B11___Lunar_Tomato_rar
127 B11 Mods: http://www.gamefront.com/files/22730491/B11_Mods_rar

Dropbox
Lockdown B11: https://www.dropbox.com/s/odjf4x5i2rd1qah/B11%20-%20Lockdown.rar
Lunar Tomato B11: http://www.dropbox.com/s/ihhb4t2qacxoce4/B11%20-%20Lunar%20Tomato.rar
127 B11 Mods: http://www.dropbox.com/s/w7s8nscmc8im4by/B11%20Mods.rar

Note: To access the buy menu, press the next actor and previous actor keys at the same time.

If these total conversions are not allowed to be posted, I will gladly take the modified content and pair it with a fresh copy of the B11 installer instead.