Teamspeak is an amazing piece of free software. While not Open Source, it does at least give you control over your data. In comparison to Skype and Discord, Teamspeak's performance is all up to you. You get to run the server, not relying on a third party to give you the bandwidth you need to have good quality audio.
Recently I have had the need to setup 4 different Proxy servers using Squid. My requirements were rather simple: each machine had 8 IPv4 addresses which needed to be able to route requests, the login needed to be simple username and password, and the proxy incoming ip was to be used as the outgoing ip. This is for a standard HTTP and HTTPS proxy, if you need a SOCKS5 Proxy please see this post (How to install Dante Server 1.4.1 on Ubuntu 16.04)
Recently I had the need to setup a SOCKS5 Proxy server. After looking at all of my options, I settled on the easiest solution (Dante SOCKS Server v1.4.1) that met all of my criteria.