1. Celephais is the forum Q1 modders meet and showcase projects:
www.celephais.net
2. Quaddicted stores hundreds, if not more Quake 1 mods:
Recommendation of the following oldskool Quake1 map-packs:
- Soul of Evil
- Nehahra Project
- Operation: Urth Majik
- The Altar of Storms
All five star map-packs on Quaddicted are worth a playthrough.
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Back in early 2000s I dreamed about working as a level designer so I was pretty interested in the modding community of Quake, Half-Life and Unreal. It was the golden age of individual modders: The engines are starting to pull off to show good graphics, yet not good enough to persuade modders to go away (modern engines take a LOT more effort to create contents for). The companies encourage modding and provide full tools (with patching) for it.
The communities are still vibrant but many left throughout the years.