Gas Guzzlers Extreme
https://gtm.you1.cn/storesteam/app/243800/Gas_Guzzlers_Extreme/
Up to 4 players if your computer is powerful enough.

Hack: LAN play on single computer using Nucleus Co-op.

Instructions: https://gtm.you1.cn/app/243800/discussions/0/1495615865212122330/

FlatOut 2
Steam: https://gtm.you1.cn/storesteam/app/2990/FlatOut_2/
GOG: https://www.gog.com/game/flatout_2

Up to 8 players in split screen (or use multiple monitors).

Hack: LAN play on single computer with the help of a mod.

Instructions: https://github.com/DeadlySurprise/FO2-Splitscreen
For Steam version you may need to do this trick: https://github.com/DeadlySurprise/FO2-Splitscreen/issues/1

Re-Volt:
Remote controlled toy cars with powerups.
Re-volt description on moby games[www.mobygames.com]

Up to 4 players in split screen.

Hack: Modified game executable.

Instructions: Install the RVGL[rvgl.re-volt.io] version.)

Wreckfest
Steam:
https://gtm.you1.cn/storesteam/app/228380/Wreckfest/

Managed to get 2 player split screen with 2 steam accounts and 2 purchased copies of the game using "Sandboxie" and "Borderless Gaming".

Instructions here:
https://gtm.you1.cn/app/228380/discussions/0/1842440600605272929/

EDIT: Nucleus coop now supports Wreckfest so use that solution since it's much easier to set up.

Thanks for the info Supersmo!

Nucleus coop helps to set up multiple instances of a game on 1 computer and arrange them so they are borderless windowed and arranged on 1 or more screens.

The solution requires more performance from the PC since the game is run multiple times.

Racing games supported by Nucleus Coop:
* Carmageddon: Max Damage
* F1 2014
* Flatout 4: Total Insanity
* Gas Guzzlers Extreme
* NASCAR '15 Victory Edition
* Need For Speed Most Wanted 2005
* Project CARS 2
* Wreckfest

Racing games that already has split screen but with nucleus can support more players in split screen:
* Dirt 3: Complete Edition
* F1 2012
* Grid
* Grid 2
* Insane 2
* Redout: Enhanced Edition
* Re-Volt (RVGL)[rvgl.re-volt.io]
* Rock of Ages 2: Bigger & Boulder
* Sonic Robo Blast 2[www.srb2.org]
* Split/Second

Nucleus Coop FAQ and current list of supported games: https://www.reddit.com/r/nucleuscoop/comments/fjdqid/list_of_new_supported_games_and_faq/