@jalict Hopefully someone comes along with an even simpler one, but if you already have or want a nextcloud instance, its Talk app isn't much *additional* effort. I originally wasn't going to bother setting up Talk when setting up nextcloud because Signal works better for my use case, but it wound up being simple enough that I did anyway. It supports joining a call without an account. It has web and mobile apps. I mostly still use Signal but when I have used Talk, it's worked pretty well.