Slave Zero surprisingly had a multiplayer mode that's largely overlooked. This re-release of the game does feature it but it crashes immediately upon launch.

There is a way to fix it, however it involves installing a Direct 3D renderer for the game.

Download the Direct 3D renderer here

http://community.pcgamingwiki.com/files/file/546-slave-zero-direct3d-patch/

After downloading it, extract the files to the game's directory. This is typically located in

C:\programfiles (x86)\steam\steamapps\Slave zero

To run the multiplayer double click the file D3d_SlaveZero.exe

note there are a few downsides to the multiplayer in this game

There are no bots

You can't customize your character

there are no custom maps

there is no server browser. It's all local.

But if you feel nostalgic over playing the multiplayer to this game, and you have friend who also owns the game you can play together.