OGMP is the OverGrowth MultiPlayer mod, an unoffical addition to the upcoming game Overgrowth by Wolfire Games.
At the moment you will need a Linux machine to host your own server. To use this project you have to compile it first:
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make
If you just want to play with friends you do not need your own server though, you can use the public server ogmp.net.
To start a server you have to run the ogmp binary:
./ogmp [bind address] [port] [htdocs]
e.g. ./ogmp 0.0.0.0 9000 htdocs
This mod is still early alpha and buggy. If you encounter a bug it would be nice to send us information about it via the issue tracker of Github. Please try to avoid duplicates though.