Depending on what you want the game to feel like, @ko6ux, I would suggest Savage Worlds as an option. The current edition (Savage Worlds Adventure Edition, commonly referred to as “SWADE”) has you covered for modern horror and some fantasy, too, just from the core book.
There are also Companions which can help refine things a bit more to your tastes with optional rules to change the emphasis in your game, for example making combat grittier or more cinematic. The first couple of these are out in PDF, and another is currently available on pre-release through crowd funding. Hard copies have been held up a little by supply issues but are coming in the next few months.
Going back to my point about the ‘feel’ of Savage Worlds - it is a game with pulp sensibilities baked-in to the core. So the fantasy is pulp-fantasy by default (closer to Lankmar than Faerun etc.) and the horror is also a bit more cinematic than literary. You can tweak it up or down, and the Companions do a great job of helping with this, as does the core book with a whole stack of optional Setting Rules which can be added in to a specific game).
The great things about a good generic system is how easy it makes it to do one-shots with different foci without needing to find and learn a new system every time.
I played a little bit of Monster of the Week and thought it was pretty decent. It’s fairly rules light, and the characters in our group covered a relatively broad range of types. I was a completely normal EMT assigned as a medic to a team that had one definitely supernatural being. When we got attacked, I relied on my best weapon: the portable defibrillator I was toting.
I would also suggest Cypher System/The Strange. Haven’t gotten to play it, though.