The following list of links should serve as a starting point to find an instance of a particular type of web service. These services are all Free/Libre and Open Source Software (FLOSS) and can also be self-hosted. If you want to try them out, but don't want to run an instance yourself, you can find public instances on the following directories, sorted alphabetically by the name of the sofware:
Discover more services on Chatons
To add additional software instance directories to this list, create a merge request for this branch in the git project. In order to qualify being added to the list, the web service directory needs to be Free/Libre and Open Source Software (FLOSS) and it should get updated at least once a week, manually or automatically. The main development branch of this project contains an example of an automated directory list service and the maintainer would be interested to expand it to cover additional web services - raise an issue per web service type to discuss this further, if you are interested in participating.