There are several, I encourage you to read the following post from the FSF:
https://www.fsf.org/campaigns/priority-projects/voicevideochat
- [Trisquel-users] Free software Replace Skype aggeliszotis
- Re: [Trisquel-users] Free software Replace Sky... dhood
- Re: [Trisquel-users] Free software Replace Sky... Adonay Felipe Nogueira
- Re: [Trisquel-users] Free software Replace Sky... Cassandra of Troy
- Re: [Trisquel-users] Free software Replace Sky... svhaab
- Re: [Trisquel-users] Free software Replace Sky... csh
- Re: [Trisquel-users] Free software Replace Sky... shiretoko
