Multiplayer is currently available at the game in just one way, 2 - 4 players on the same computer.
There is not internet connection, both LAN and WAN conections are impossible in the game at the moment.
How to play multiplayer ?
Player 1 will use the keyboard as usual, but you can connect through USB cables computer gaming controllers or XBOX 360 controllers to your laptop/computer and the game will recognize them and you will be able to play with your friends in just one screen.
Are ps3 controllers recognizeable by the game ?
No, ps3 controllers wont work with the game, unless you download some programs that will make your computer ( and obviusly the game ) think that the ps3 controller is an XBOX 360 controller, however it takes time to get it to work perfectly but people that have done it say its worth it, however it is recommended to buy XBOX 360 controllers if you dont have one, a cheap one if possible.
If i dont have and cant a buy a computer gaming or XBOX controller ?
Unfortunately you wont be able to experience the fun of multiplayer, however it has been mentioned several times on the official cobalt forum that using Motionjoy will let you play Cobalt with ps3 controllers, if you dont have ps3 controllers...then you cant experience the fun of multiplayer until the online multiplayer comes out.
The future of multiplayer
Oxeye Game Studios have already made us aware of their interest of an online multiplayer, information is found here : http://www.oxeyegames.com/no-networking-shenanigans/, but also it will take some time and hopefully we will have online multiplayer by beta.