Reddit, the name alone might strike fear in a lot of people. True there are some dark dark corners of it sure, but there are some bright spots one being the /r/monsteraday/ subreddit
It’s an D&D subreddit that focus on making home brew monsters to move into your 5th edition game.
They have released a PDF of all the monsters so far, it’s designed to make it look like the Monster Manual. With stat blocks and artwork. It’s VERY high quailty and well put together.
You can download the full 102 page PDF Here
The PDF is updated as they add new monsters as well. (The PDF tends to be a few days behind, but they get added)
As far as fan created projects go, I must say this ranks up there with the best of the best.