Добавил: The DSystem
After seeing some pictures of the beta version I decided to port the original models, with exception the Doctor Keller and Barney are re-textured due to my lack of experience in modifying the skeleton models.
1 - Extract the folders with "_addon" on the Half-Life folder.
(Example: C: \ Program Files (x86) \ Steam \ steamapps \ common \ Half-Life)
2 - Once the game starts, check the options, and in the video tab check "Allow custom addon content."