If you wanna play with a friend on Road Redemption without splitscreen, that's actually possible, but kinda messy in the menus.
All you need is 2 screens (ofc) connected to your computer, and make the one above the other as main screen in the windows menu (google it if you need, it's easy)
Then, go to Steam, Road Redemption, and set the actual argument if you have two 1080p screens
Right click on Road Redemption > Properties > Launch Options (Thanks B Dawg for this part I forgot)


As you will see, the game should take both your screen. However, you better know where you're going, because the only downside of that is that the menus are not really scaled, but in game, there's no problem. Been playing classic with my gf all afternoon and it worked well. Not sure for the campaign menu.

Finally some "fullscreen" multiplayer, even if it's local. I don't know if it'll work for more player, but you might have a start with that.

If you wanna see how it's looks, head here: http://imgur.com/a/3WynW

Have fun