I want to know if there are other specialised Q&A sites (and not general-purpose like Quora). I feel Stack Exchange has a monopoly in this domain. Since it’s both hosted in the US and its business model is not very clear (look at the trackers they have on their site), I want to avoid using it to ask questions.

I’m actually considering hosting my own French Q&A site that specialises in mathematics (from kindergarden to graduate), using libre software and relying on donations.