Resources for generating a navmesh?

So I was interested in learning about doing pathfinding in a 3D world, but my google-fu couldn’t get me past knowing that I needed an navmesh and general idea of what the mesh represented.

I was just curious if any of you knew of any good resources for them (I tried looking for the source for one in a 3D game library, but they were either closed source or there were so many packages and folders and classes that I got lost).