Recs.
Updated
SpecsUpdate
Pros
Pro Very good multiplayer support
Urho3D has the best multiplayer support at least among free engines. Most importantly, Urho guys do understand importance of authoritative servers for any serious development. In particular, Urho supports such features as Interest Management and hooks for Client-Side Prediction.
Cons
Con May be a bit hard to get started
To install Urho3D you need to get the archive from GitHub (be careful to download the master branch) and extract it. After that, you need to compile the engine with CMake. If all the dependencies are installed, then it should be a straightforward process, otherwise you will need to track down and install all the missing dependencies.
For people who don't have much experience with CMake this whole process may seem a bit like magic. For people who do have experience with CMake, the whole installation will be relatively easy.
Con Little documentation and small community
There are some high-level design docs and a bunch of examples, but code is poorly commented and nothing much more can be found.