CNC Renegade supports both online play (via Westwood Online) and multiplay via Local Area Networks; some of the multiplayer options that exist are below:
Join other players online and fight one another in arena-style Death Matches.
Renegade: Command & Conquer mode
Renegade: Command & Conquer mode, or "C&C Mode", is a multi-player game where two teams of players - GDI vs. Nod - attempt to destroy the other's base. Each base functions in a fashion similar to a typical Command & Conquer base: Harvesters gather Tiberium and take it to the Tiberium Refinery for processing, Power Plants supply power to other base structures, etc. As part of the game, you can 'purchase' different character classes (Engineer, Rocket Soldier, etc.) and vehicles (Tanks, Buggies, etc.) with credits earned from kills or from Tiberium processed from your Tiberium Refinery. To win, you must destroy all of your enemy's base buildings or place the 'end game' beacon (Ion Cannon or Nuke) in the enemy base.
You may also wish to check out RenGuard, an anti-cheat utility for Renegade.