I enjoyed this GTA-esque style game and loved blowing everything up. I always thought it would be a lot more more fun with Multiplayer. Well, the community have only gone and modded it to have multiplayer!

https://www.jc-mp.com/

It's Beta at the moment but there is a 5000 man server available. I jooind when it had 497 people and (very) surprisingly it was not too laggy either!

Taken form the wiki:

Features:
- Scripting system using the simple but powerful Lua language. Use server-side and client-side scripts to create anything from a spawn menu to entire gamemodes.
- Server browser allows you to easily find a server and keep track of your favorites.
- Steam authentication: your JC2-MP account is tied to your steam account, which allows servers to keep track of players by Steam ID.
- An optimised network streamer means a server can support thousands of players and vehicles across Panau.

What's synced:
- On-foot movement
- On-foot weapons
- Vehicle movement
- Vehicle weapons
- Vehicle mounted weapons (such as turrets in jeeps)
- Vehicle spawns
- Vehicle colors
- Vehicle damage
- Stunt position
- Time
- Weather
- Character models

What's not synced:
- Fixed Mounted Guns (Cannon / Flak Cannon / Fixed Mini-Gun)
- Parachute
- Grappling hook
- Persistent destroyed structures
- Unoccupied vehicles
- Thrown explosives and melee

As JC2-MP is in development, you can expect this list to change.