-> Jami (according to their website, I only ever used their chat and regular one-on-one calls)
-> Wire (client and server open source, but not community-lead development)
-> WhatsApp (if you trust Facebook, proprietary back-end)
And if you consider open source & on-premises / "can be completely locked off from the Internet so only you can access it" software to be end to end encrypted (if you personally run the server, you're one of the endpoints):
-> Jitsi Meet (full e2ee is under development, collab with Matrix I think)
-> BigBlueButton
-> Apache OpenMeetings (I never used this one, can't vouch for it)
Signal and Threema don't do group calls as far as I can quickly find online, correct me if I'm wrong.
Anyhow, plenty of options whether you like to self host (saves a ton of CPU on encryption and lets the server do stream mixing) or have full end to end encryption. Why do you care whether they're used by a billion people / "popular"? You can still choose to use them and improve the status quo because why not?