Mumble is an open-source, low-latency, high quality voice chat
...Low-latency and high-quality voice-chat program written on top of Qt and Opus. Administrators appreciate Mumble for being able to self-host and have control over data security and privacy. Some make use of the extensive permission system for complex scenarios (for example separating two groups but leaders being able to talk to both). Some love to provide their users with additional functionality with scripts making use of server APIs, or host music bots and the like that connect to the server. Those that have an existing user database often make use of authenticators to allow authenticating with existing account login data.
Ever wanted a GOOD IRC client, but couldn't find one? Maybe some didn't support the platform you worked on, or maybe some didn't present the interface YOU wanted. Look no further. Free IRC is a project to build an easy-to-use, and yet complex, client.