Minecraft is a great example, being split into two code bases for different purposes. Minecraft Java was the orignal platform and is supported by a large community providing modules, most of which can be accessed for free. There's a strong correlation to WotC D&D's original intent with the OGL here.
Minecraft Bedrock was developed for cross-platform and has the Minecraft Marketplace for paid expansions, from both Mojang/ Microsoft and 3rd parties. It's all optional, but its easy for kids to overspend on their parents credit cards and has recieved criticism for being "predatory".