Fernando, I cannot attest as to whether these follow suckless design philosophy, but the following are voice related programs from a list on the topic of FLOSS Educational Resources for Internet and Distance Learning:
https://www.mumble.info https://f-droid.org/packages/se.lublin.mumla/ Mumble is a free, Open Source, low latency, high quality voice chat application. Mumla is an Android app for the Mumble voice conference system. Mumble can handle 1000 concurrent users. http://llcon.sourceforge.net/ Jamulus software enables musicians to perform real-time jam sessions over the internet. Latest version can handle around 100 concurrent users playing together. Hosts at least 50 concurrent users. https://sonobus.net/ Sonobus is an easy to use application for streaming high-quality, low-latency peer-to-peer audio between devices over the internet or a local network. 12 concurrent users maximum. As for screen sharing, you already mentioned Jitsi and there are some programs that allow for collaborative editing. Wouldn't consider any of them lightweight or suckless. You can find the list here: https://lmemsm.dreamwidth.org/14124.html I'd be very interested in adding other options to it, if anyone has other software recommendations for it.
