surviv.io is described as 'Players are represented by circular figures on a 2D grid-like playing field, surrounded by a circular "red zone" that shrinks as the game progresses'. There are more than 10 games similar to surviv.io for a variety of platforms, including Windows, Android, Online / Web-based, Playstation and Xbox. The best alternative is PUBG. It's not free, so if you're looking for a free alternative, you could try Fortnite Battle Royale or Apex Legends. Other surviv.io like games are Rules Of Survival (Free), Last Man Standing (Free), H1Z1 (Freemium) and Vertix Online (Free).
PLAYERUNKNOWN'S BATTLEGROUNDS aka PUBG is a multiplayer, first-person battle royal shooter set on a massive, 8x8 km island where players must fight to locate weapons and supplies to survive a battle and remain the last man standing.
Fortnite Battle Royale is a 100-player PvP mode in Fortnite: Save The World that is free to play. One giant map. A battle bus. Fortnite building skills and destructible environments combined with intense PvP combat. The last one standing wins.
"Slay.one" is a free multiplayer top-down shooter which you can play directly in your browser - no install required! Features the game modes Deathmatch, Team Deathmatch, Ranked, Zombie Deathmatch, & Capture the Flag!