Jazz Jackrabbit 2, the game responsible for myself and @Nimrod meeting and eventually founding Digiex is currently free on Good Old Games (GoG) for the approx. the next 52 hours from the time of this post.
Jazz Jackrabbit 2 is a 1998 platform game produced by Epic, who are better known for the Unreal Engine and Fortnite games these days. The game is a 2D side-scroller that incorporates elements of shooting and platforming. The player must venture through a series of levels populated with enemies and environmental hazards that may hinder the player's progress.
Where Jazz Jackrabbit 2 really comes in to its own is the multiplayer. Multiplayer features five game modes, Cooperative (where players work together in the game's single player campaign), Battle (which is basically Deathmatch), Race (in which the first to complete all laps wins), Treasure Hunt (in which the first to collect 100 diamonds and find the exit wins the match) and Capture the Flag.
The game also includes a level editor, allowing anyone to create custom levels for the game with little knowledge required to master the basics and get started.
Trivia: Digiex has hosted the list.jazzjackrabbit.net list server for almost the last two decades, allowing multiplayer games to be found from within the in-game list, without patching the game to use an alternate server.
To conclude if you have any interest in 2D platformer games like Sonic or Mario, it's well worth checking out Jazz. The online community is still active today, 24 years after the release of Jazz 2.
Claim: Jazz Jackrabbit 2 on Good Old Games (Includes the The Secret Files & Christmas Chronicles Expansion Packs)
Discord: Jazz Jackrabbit Community Discord