Matthew Butterick of Practical Typography nails it:
- Open source arises from a spirit of capitalist competition.
- Open-source developers are paid.
- Open source redefines what is valuable.
- Open source relies on meritocracies.
- Open source relies on benevolent dictators.
- An open-source project requires multiple developers.
- Open source is part of the project’s DNA or it’s not.
If these are not met, he says, it’s not open source it's just file sharing.