I'm in the mood for some old school horror games for PC. Which horror games for DOS (from GOG's library or even some freeware/abandonware games) would you guys recommend to me?

Alone in the Dark Trilogy

Thanks! I totally forgot that you can filter the search page, haha.

Dark Seed
Dylan Dog: through the looking glass
Veil of Darkness

Well.
Does Hugo's House Of Horror count?

The Legacy: Realm of Terror

Don't go Alone: A game similar to Dungeon Master and Legacy. Dungeon Crawler in a haunted mansion. I wish It were available someday in GOG. If I am not mistaken it is from 1989 more or less.

Shadow of the comet: Lovecraftian classic story. And a classic point and clck adventure. Pretty hard.

Waxworks

And as a couple folks above me mentioned;

Alone in the Dark 1,2,3
Dark Seed


Good luck

Add to the mentioned:

D

Phantasmagoria

Phantasmagoria 2

And others aren´t on gog:

Are you afraid of the dark?

The Dark Eye

The Dark Half

Bram Stoker´s Dracula (1993)

Space Hulk (1993) - A squad tactics proto-FPS hybrid with limited pausing features (there's a top down view where you can give out orders during a time limited pause).

Realms of the Haunting (1997) - FPS

Last Half of Darkness (the original, EGA graphics-based one) has always been a favorite of mine.

I would second Veil of Darkness, great game, loved it!

To add to the suggestions already made: Elvira II Jaws of the Cerberus and Elvira I Mistress of the Dark. In addition I would recommend Ecstatica and maybe ZombieVille which both belong to the survival horror genre.

Edit: Nocturne isn't a DOS game so I edited it out. ;-)

https://www.gog.com/game/personal_nightmare

https://www.gog.com/game/gabriel_knight_sins_of_the_fathers

https://www.gog.com/game/call_of_cthulhu_prisoner_of_ice

Ecstatica 1 and 2:
Two forgotten games from the Alone in the Dark era. They were created by a single person (At least the first one) and he developed some kind of 3D voxel engine with prerrendered backgrounds for an action adventure that was relatively popular in the era. It was singular by the rounded style of graphics. The concept of the engine and gameplay was similar to alone in the dark and others like little big advenure.

They are not available anywhere legally, if I am not mistaken.