Sonic Frenzy Adventure is a retro-style fangame developed since 2004, featuring 11 zones and 5 playable characters, including two original ones. The game introduces unique mechanics such as a revised ring system with four levels, various shields with passive effects, and special powers exclusive to Sonic. Players explore each zone, ending in a boss fight, with a storyline focused on defeating EggRobo's mechanical empire. Achievements track high scores and hidden collectibles, and the game offers character-specific routes and challenges.