I know of one but it's niche. OpenSubtitles allows people to pay for ads at the start/end of content when you download subtitles on the fly. I've seen countless NordVPN ads in subtitles.

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everybodyknows 14 hours ago | parent [-]

Another niche: Software professionals

https://www.carbonads.net/

	▲	hunterpayne 7 hours ago \| parent [-]
		Have you used them? How was your experience? Did the ads convert effectively?