Note:

Just like our release of Quake, we made sure to include ALL mods/addons/DLC
(call them whatever you want) currently available. No online connection is
needed.
To make it easy for you, we relinked the download partition to the actual
1.08 update so the game will see them as pre-installed. You can find them
in the “Addon” menu.
Addons available:
– Earthless: Prelude
– Syringe
– DOOM Zero
– REKKR
– BTSX: Episode 1
– BTSX: Episode 2
– Double Impact
– TNT Evilution
– The Plutonia Experiment
– Deathless
– No End in Sight
– SIGIL