XcomUtil
ufopaedia.org
ufopaedia.org
Good times, and a testament to the flexibility of the engine.
I also played the 2012 sequel, XCOM: Enemy Unknown, but it (for me) just didn't have the same magic.
I found it was close to the original, but too slow/buggy.
That said, XCOM save files were my first recipe-following introduction to the arcane world of hex-editing.
Always wonder where they get their "recruits", who seem to have trouble with aiming their weapons towards the enemy.
There's an open-source & cross platform remake of the engine. You still need the original game assets.
Easy to mod - he config files are YAML.