I mean, I’ve listed the alternatives all in the other forum thread FireRTC is dead - use BobRTC
If you want to do general purpose calls like calling your friends & relatives, try out TextNow (https://www.textnow.com/messaging). It’s easy to use, has an open dialpad and allows free calls to US, Canada, Germany and UK but requires you to be from US/Canada to be able to sign up for it. They have smartphone apps but also a web interface to make the calls. If you’re not from the US, ask a friend who is from there to create an account for you. Downside: hard to access if you’re not from US/Canada, you cannot change your callerID on every call.
If you need something to spoof your callerID to something specific, try out SIP services like voip.ms, Flowroute.com or plivo.com. Benefits: professional use, tons of features, call routing, callerID spoofing, buying numbers is pretty cheap. Downside: they are paid / you’ll need a credit card and you’ll need to use a software phone like Linphone, X-Lite or MicroSIP.
You could also just use Skype.