Definition of independent for the purposes of this question: source is not owned by a for-profit corporation, is not financially backed by any billionaire (either directly or via foundation or nonprofit organization) and is not financed by any national government (even if run without oversight).
It can have any perceived bias or political leaning.
Edit: Just to add it has to be written in English.
Mother Jones is run by a nonprofit funded by reader donations. I’m sure some billionaires probably donate to it, but so do others.