Here is the full list of all 13 GabeN: The Final Decision achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Destroy the Combine Tank guarding the eastern gate!
Congratulations! You beat GabeN: The Final Decision! Feel free to uninstall.
Ok so now you defeated the Illuminati! Congrats! Now you can release Half Life 3! Or can you...
Finally, you defeated the Illuminati! Or did you...
Kill the last admin alive, Wallace Breen.
Kill GLaDOS and shut down her systems.
Kill the Administrator before she relays her dangerous information to the rest of the admins!
KIll that commander with your sick burns! (Mixtape not included)
Utterly destroy that illuminati boss!
Completely wreck that commander!
Defeat the Xen Leader, Nihilanth!
Defeat that traitor!
Unlocked by starting a new game.