Mindustry has an interesting commercial model - the entire game is available for free and is fully open source - with players able to download from itch.io or build from source themselves. They can also purchase it for a reasonably nominal cost on Steam to support the developer. They don’t get any additional in-game functionality, but do get automated updates and access to the Steam Workshop for managing their mods.

This is a cool model. You can still play the whole game, but now the dev doesn’t have to write an auto-updater and people who truly can’t afford to pay can still get the full functionality.