Discord competes with Teamspeak, Mumble, Ventrilo, and Skype in the category of gaming voice chat, but it also offers an interface set up like Slack, which has gained popularity for topic-based persistent chat. It hits a sweet spot of good-enough voice & text chat that's cost-free, needs no configuration, is fully hosted with captive servers, uses decent codecs, supports inbound hyperlinks, has a slick UI, has official same-name clients on mobile, has a web client, and the like.
Discord's rise helped by Microsoft's seeming neglect and confusing platform direction of Skype in recent years, even if Discord still doesn't have video chat. For messaging among people who know each other by name, Facebook's offerings are dominant, but for pseudonymous chat Skype remained strong until Microsoft vacillated between making Skype Windows' native messenger or a strong multiplatform freemium network that isn't plagued by an aging UI and the invasion of advertising. Discord won many users by organic word-of-mouth referrals from people who used to use Skype.
As for gaming voice chat, Discord is not as sophisticated as other offerings (edit: maybe that's the wrong wording; let's go instead with "not as configurable"), but offers a smoother out-of-the-box experience.
Discord isn't about to replace TS/Mumble for your WoW raiding or large organized clans, but it spread like wildfire among my friends who play League of Legends or Dota 2, and other games with medium-small groups of players.
The fact that you don't need to install or configure any client (or even have an account) to bring someone in is the biggest single thing.
People come for the easy invites and stay for the (slightly better than) good enough chat, voice, and community features.
My experience has been that Discord has utterly replaced TS/Mumble/Ventrilo for WoW raiding.
I'm sure there's plenty of guilds around that are still happy with their existing setup and haven't bothered switching, but my experience is that many have switched, and new guilds are basically only picking Discord.
Discord isn't about to replace TS/Mumble for WoW raiding because it already happened. Discord doesn't have 100% of the market or anything, but it's definitely the most common.
It _has_ replaced TS/Mumble for ffxiv, voice chat for subreddits, other game communities. WoW is bigger and has more inertia, but the network effects are strong.
I can see it pulling away from pretty much everything except those groups that have spent lots of time on crazy teamspeak setups with lots of ranks, different overlapping groups and so on.
>> except those groups that have spent lots of time on crazy teamspeak setups with lots of ranks, different overlapping groups and so on
Is TeamSpeak an open API? Shouldn't be difficult at all to write an import tool to import a TeamSpeak server's group structure to equivalent Discord roles.
It isn't, and Discord's group structure is less flexible. For example, any rank with the ability to assign ranks can assign any rank below it. In comparison, a teamspeak server has different groups and people can only assign people to their own groups.
Ultimately, I don't think this is as much an obstacle to long term success of Discord. These kind of servers tend to come around because running TS/Mumble servers require expertise certain groups don't have, so groups tend to colocate over some overlap in membership, and may still be colocated over inertia even if the overlap goes away.
The example I'm thinking of is a server I'm still on which is nominally owned by a battlefield clan, but also has a ffxiv guild, wildstar guild, eve corp and minecraft server chat on it. Each of these are effectively seperate entities and need to manage their own permissions, and if they were setting up fresh now, they'd all be seperate discord servers. The battlefield guys have some crazy rank structure based on time on the server or some such, the ffxiv group just has admin or not, and the minecraft group is a yes/no access perm.
The colocation is particularly not ideal as the battlefield clan and minecraft server tend to bring occasional DDoS attempts on the server, and there's not really much overlap in membership nowadays.
It has recently become the ease-of-use choice for our RPG group. Being a mixed group not everyone is used to configuring clients etc. so the out of the box usability is definitely what works for us.
From the DM point of view he can still send us pictures, it is free and we don't really use maps so don't need Roll20 (or equivalent). Also direct messaging players secret messages is really easy and handy.
Discord's rise helped by Microsoft's seeming neglect and confusing platform direction of Skype in recent years, even if Discord still doesn't have video chat. For messaging among people who know each other by name, Facebook's offerings are dominant, but for pseudonymous chat Skype remained strong until Microsoft vacillated between making Skype Windows' native messenger or a strong multiplatform freemium network that isn't plagued by an aging UI and the invasion of advertising. Discord won many users by organic word-of-mouth referrals from people who used to use Skype.
As for gaming voice chat, Discord is not as sophisticated as other offerings (edit: maybe that's the wrong wording; let's go instead with "not as configurable"), but offers a smoother out-of-the-box experience.