Polytoria is described as 'free-to-play platform and website similar to Roblox. You can create levels, play levels, talk in a forum, customize your avatar and do many more activities'. There are four games similar to Polytoria for a variety of platforms, including Windows, Mac, Online / Web-based, RBXLegacy and Roblox. The best alternative is Roblox, which is free. Other Polytoria like games are Novetus (Free, Open Source), WorldToBuild (Free) and Oziverse (Free).
Roblox allows you to create games, build whatever you want with lego-like bricks, play other games made by users of the community, and even participate in the economy by trading, selling, buying, and collecting items.
Tired of the roblox tyranny and greed? The Novetus community game is the solution! Novetus was made to improve on RBXLegacy, with the addition of new features that enhance the launcher for mod development, player customization, and overall usability.