EthicalAds is our ad network for sites not hosted by us and it's about a month old. It uses the same ad serving setup as Read the Docs and it follows the same principles.
Based on my affiliation, I'm going to be biased. However, if you have any questions, you can reach me at my first name @readthedocs.org.
[1] https://docs.readthedocs.io/en/stable/advertising/ [2] https://blog.readthedocs.com/archive/tag/advertising/
https://www.carbonads.net is by buysellads, which I have a generally mixed opinion of.
There was a similar company called codefund, which has recently shut down and now redirects to ethical ads.
All of these are for tech publications and have moderately rigorous applications, with requirements for content and traffic.