I have started to create an editor for creating navigation meshes.
What is already done:
Loading of the scene
Choosing meshes to be used for the navmesh
Tweaking navmesh parameters in realtime (solo/tiled navmesh supported)
Realtime crowd testing by Adding/removing agents for testing
Realtiime computepath by Adding/removing/moving starting and ending point for path generation (direct/smootth path supported)
Realtime obstacle editor
Navmesh toggling
Navmesh wireframe toggling
Exporting the navmesh data
Importing of the navmesh data
To be done:
Computepath with multiple points
Individual crowd agent properties
Tweaking individual custom areas of the navmesh
Offmesh connections editor
Heighfield debugging
Heightfield walkable debugging
Compact heightfield solid debugging
Compact heighfield regions debugging
Compact heightfield distance debugging
Raw contours debugging
Contours debugging
Polymesh debugging
Polymesh detail debugging
Navmesh BV tree debugging
If this gets enough votes I will consider to upgrade this already handy tool to a full-blown visual editor.
This is useful! It can be such a pain to get the right combination of parameters.
Reachability analysis would also be cool checking whether there aer unreachable mesh islands.
What do you want to edit? The vertices on the navmesh? I wonder though if this is worth the effort. Because once you have figured out the right params for your project, you should not have to worry about the navmesh anymore. If you need further editing, the params are probably off.
. And then, not everyone needs a nav mesh. I’m sure it would be a great addition 
You’re always so nice!