Mlem is licensed under the Commons Clause, which prohibits commercial use, even though the project advertises itself as “open source”.
The maintainers have refused to accept PRs that change the wording to “source-available”, edited comments and locked threads about the topic:
While i generally don’t mind about this kind of things, indeed, on the main page of common clause there is a FAQ saying to not call Open source https://commonsclause.com/