Discord
Discord is a free-to-use VoIP and instant messaging app targeted primarily at gaming communities.
-PRO Can be used in browser
Users can invite others to join a Discord channel via a web link, which means no installation is required to use the software - which is one of the big typical barriers to entry for social software.
-PRO Accessible to anyone
Discord is partially free
-PRO Easy setup
You can quickly send invites to people and they can join
Mumble
-PRO Excellent voice quality
Since version 1.2.4, Mumble uses an audio codec named Opus that's specifically developed to provide low-latency voice communication over Internet. This means that there is no delay time, while audio still comes out clear.
-PRO Low latency and resource usage
Dedicated servers
-PRO Code available to anyone to inspect or use, no spy- or adware
Mumble is available as a free
TeamSpeak 3
-PRO Works on all main PC OS platforms
Available on Windows, Linux and OS X allows for a user to choose what best OS suits them and not have to worry if their game chat software will work.
-PRO Widely used
Among most MMOs
-PRO Supports audio and text chat
TeamSpeak allows for both voice and text chat
Google Hangouts
Available directly in the browser (requires plug-in), or as a Chrome app, or as a mobile app for Android and iOS.
CON Not focused around gaming
Hangouts is a general chat application, and as such it doesn't offer any specialized gaming features. It won't connect into any games, it doesn't normalize audio, there is no positional audio, or any other features gamers would appreciate.
PRO Most people already have an account
Many people already have a Google account
CON Requires a strong internet connection
Blizzard Voice Chat
Blizzard voice chat makes it possible to chat with your friends through the Battle.net client. You can use it in any Blizzard game.
CON Can only chat with friends and friends of friends
Though it might limit the amount of unwanted rude people in your chat, it does limit the functionality in some games, where chatting with randoms would be beneficial.
CON Bad voice quality
PRO Built into the Battle.net App
Curse Voice
PRO Completely free - not even a server is required
Unlike other popular VOIP gaming services there is no need for a server to use this app nor is there a cost to use it. It is completely free for anyone to use at all times.
CON Changes could be coming soon
Twitch (which is itself owned by Amazon) has recently bought it
Omlet Arcade
Arcade is a social network for mobile gamers on Android and iOS. It has free unlimited voice chats with your groups. It also lets you live stream, capture videos, find gamers who play the same games as you, and much more.
PRO Crisp design
Like new theme
PRO Many additional functions
Livestreaming, multiplayer, mods for Minecraft,
PRO Small < 10MB
Ventrilo
CON Hasn't been updated in years
Barely works in compatibility with newer operating machines and the instructions for setup are somewhat outdated
thermoplastics
CON Requires a server to use
CON Lacks a Linux client
C3
C3 is a completely free to use voice and text chat application made for gamers. It was created by Vivox, who have and continue to provide integrated voice services for some of the more popular AAA games on the market. It can be used for MAC and PC.
CON Busy UI
The C3 UI is busy with lots going on. There are multiple tab arrays, channel dropdowns, and many buttons. This all leaves the chat section a very small portion while it is actually the more important function.
CON Little dev support
The last time the website was updated was 2014, and there doesn't seem to be any activity by the devs lately.
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PRO No need to host a server
GameVox
CON Limited locations described as "NA", "EU" and Asia Pacific
Only North America, Europe and Asia Pacific locations have servers. The location isn't specific either, meaning players on the West coast of North America could have a server on the East coast, which can cause latency. If service went down you would have to change to another continent as there...
PRO Persistent chat rooms
CON No Mobile version yet
Skype
Skype is a very popular cross platform freemium voice-over-IP service and instant messaging client.
CON Known for exposing user IP
This is bad for gaming as can result in DDoS attacks and detecting user location.
CON Client for Linux lags way behind Mac and Windows
CON Resource hog
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