Does Nosgoth exist?

You wouldn't be able to play it. Nosgoth has been shut-down between May 31st, 2016 and June 1st, 2016. The developers of the game talked about it in this post on the official forum of the game:

May 31st – Nosgoth will go into maintenance for the final time at 11:59 PM PDT. It will no longer be possible to log into Nosgoth after this point.

June 1st – Nosgoth game servers are taken offline. (Those who log in prior to maintenance on the 31st may be able to continue to play until this point).

So there is no way to play to this game anymore nowadays.

Those keys that you can find on Google are most of the time from really old posts (2014 for a lot of them), or probably from sites who didn't think about removing them now (or are not even aware of the game not existing anymore). This Humble Bundle collection has also been there since a long time now. It seems that the content of it hasn't been modified since then, so it's probably an error from them. If you would get such a key, you couldn't do anything with it.

Sadly that game has been announced dead by its creators. To clarify, it was a 5v5 PvP with asymmetric classes, segregated into Humans and Vampires.

I loved that game to bits while it was alive and to day I miss it. I believe the reasons for its demise was not lack of unique features, bad design or boring gameplay, but mostly failure of marketing leading to declining playerbase, in a game that already has a steep curve.

I still keep the Nosgoth binaries as a memento and a slight hope that something can come out of that (even with my sub-par reverse-engineering skills). I really wish Squire Enix and Psyonix decided to at least sell the IP if not release it open-source for free. Nosgoth had a small playerbase but a large part of it really cared about the game.

Pity you never got to try it, I notice the game often seemed to be either a person's exact cup of tea or not at all.