We would like to use an interactive system for polls in our lectures. What would be alternatives to ahaslides.com that are e.g. opensource or self-hostable?
A (German) blog post by the PINGO developers mentions that using the source code, you can technically host an instance yourself, however, they don't offer any support.
I don't know about open source, but as I understand it, Kahoot!, Google Forms, Poll Everywhere, Slido, and Mentimeter are all integrable into Google Slides, and all have free tiers that allow you to do what you are asking for.
The advantage of the freemium services is that they are simple and tend to work out of the box.