Tony Cannon, the creator of GGPO (or Good Game Peace Out in full) has released the GGPO SDK under an MIT License, essentially giving devs the go-ahead to use the netcode for both commercial or non-commercial purposes in their own online games.
GGPO was created as a fighting game player's reaction to unsatisfactory performance in online matches, and as such aims to cut down on lag as much as possible in those online matchups by using rollback networking.
While all matter of online games can benefit on the player side from as little lag as possible, fighting games in particular rely on quick inputs and responses to on-screen actions, making smooth play vital for online matches.
“Traditional techniques account for network transmission time by adding delay to a players input, resulting in a sluggish, laggy game-feel,” explains the GGPO GitHub page. “Rollback networking uses input prediction and speculative execution to send player inputs to the game immediately, providing the illusion of a zero-latency network.”
Prior to this drop, versions of GGPO have helped power online matchups in fighting games like Skullgirls, Killer Instinct, and Street Fighter III: 3rd Strike Online Edition. Devs curious to find out more about GGPO can read more on its website or, for a more hands-on approach, check out the SDK themselves over on GitHub.