A couple of additional ones to look at: DemocracyLab https://democracylab.org
Civic Tech Field Guide https://civictech.guide
Also, I would suggest that context is as important as your technical skills. If there are nonprofits you are already familiar with, consider just approaching them to see if volunteering your tech skills is an option. Tech people looking to volunteer their skills often (IMO) overestimate the value of skills matching.
