Gaming communication and collaboration made easy. Discord is the place to go if you need to setup comms for a firefight, a raid, or peaceful games with friends.
Instead of using older voice apps that are more about the phone call than anything else, Discord is pretty much what happens when social media can truly keep communities in their own groups. Even if no one uses the voice calls, you can setup a Discord server to be the community itself; a replacement if not a simple backup for forums or Facebook groups.
The only real downside is the voice quality. Discord is free, and it does so by being able to handle a lot of content (mostly text and pictures) efficiently. The voice codecs are at a specific, acceptable level if you're using the free version.
For most people, that's more than enough. It's better than Ventrilo or Teamspeak from the old days unless you make some configuration changes. With Discord, the quality is great out of the box.
Mumble and Skype are the only voice qualities that possibly give Discord a run for its money. Skype's quality can be shaky or great depending on everyone's connections, and Mumble's basic quality is far better than Discord's. However, Discord handles the chat room and community aspects better than all of its voice competitors.
If you're an audiophile and must have the best voice quality on the market, you (or the community) simply need to pay for it. The server boosting system unlocks higher voice qualities, and anyone can pay for it.
It's pretty much microtransactions at that point, but the quality level isn't required for most people. Most people haven't unlocked the full potential of any voice apps on the market, so Discord just accidentally makes a lot of great tools available for easy use.