When comparing IMO vs Mumble, the Slant community recommends Mumble for most people. In the question“What is the best team chat software?” Mumble is ranked 10th while IMO is ranked 20th. The most important reason people chose Mumble is:
Mumble is available as a free download and source code is available on [GitHub](https://github.com/mumble-voip/mumble).
Ranked in these QuestionsQuestion Ranking
Pro Video call support
Pro Beautiful User Interface
Although IMO has a comparable, and in some cases superior, feature set when compared to the competition its key selling point is its interface.
From LifeHacker when it won "Best IM Client":
Signing on, navigating chats by tapping the tabs at the bottom, searching for buddies, and virtually any other operation is easy to find and use. The app, itself, is very quick. Even sending a voice IM, if you don't feel like typing, is responsive and sends quickly. Everything imo does it does well, but it's excellent navigation really makes it top notch.
IMO also has a fully functional website that you can use for chat while on your desktop or laptop. This really puts IMO ahead of the competition as you can use the same system on all your devices so you don't have to deal with overlapping notifications etc. (Note: IM+ also has this feature)
It should also be noted that it has the highest rating in the App Store due to both the UI and its stability.
Pro Easy to switch between conversations with tabs
Tabbed chats make it easy to switch between conversations
Pro Lists and chat histories are searchable
Both your buddy lists and chat histories are searchable.
Pro Accounts can be linked so you don't have to sign in to several accounts
Pro Push notifications
Pro Concurrent sessions
Concurrent sessions allow you to be logged in on your desktop while also being logged in on your phone.
Pro Chat groups
Pro Code available to anyone to inspect or use, no spy- or adware
Mumble is available as a free download and source code is available on GitHub.
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 and low overhead allows Mumble to have the least delay between users speaking and others hearing their speech, which can be very important for fast paced games.
A push-to-talk key allows you to only transmit audio when you want it. Others won't hear you chewing or your mom entering the room unless you want to.
Pro Easily overlay over game
An in-game overlay can be enabled to show users in the channel or users talking. Overlay can be disabled completely or on a per-game basis by going to Settings->Overlay. This allows for users to see their chat but not obstruct the game they are playing.
Pro Can be used on a gamers preferred platform
Available on Windows, Linux, OS X, Android and iOS which allows for the user to choose what operating system works for them and still be able to use Mumble.
Pro Free to download and use as a client
Mumble is completely free, even hosting your own server.
Pro Free and open-source server software
The server software Murmur is licensed under a free and open-source BSD-style license.
Pro Use of certificates offers more security and easy people management
Mumble uses certificates for user identification. A certificate can be generated by the user himself or issued by a third-party organization with organization certificates having 2 classes. A self-generated certificate is not tied to anything, a Class 1 certificate is tied to an e-mail address and a Class 2 certificate requires proof of identity. Depending on the server a different level of certification might be required.
Pro Server works on Raspberry Pi
Mumble server side is easy to setup and works smooth even on Raspberry Pi, which is pretty short on resources.
Pro Positional audio
Mumble supports positional audio for over 50 games, including versions of Call of Duty, Battlefield and Counter-Strike. This allows you to hear the audio from the direction of the player speaking, making gameplay more immersive and giving competitive players an edge. You can find a full list of supported games here.
Pro Secure & encrypted
This encryption is mandatory and cannot be disabled. The so-called control channel, which transports your chat messages and other non-time critical information, is encrypted with TLS using 256 bit AES-SHA. The voice channel carrying speech and positional audio is encrypted with OCB-AES 128 bit.
Pro Good audio normalization
Mumble includes great automatic volume adjustment functionality that can be used to prevent big volume changes while still allowing good communication.
By default, only users in the same channel can hear each other. Channels can be nested to better organize yourself according to what you want to be talking about.
Pro Portable version on PortableApps
Pro Server can be put on alternative firmware wireless routers
Con No support for third-party instant messaging networks
On March 3, 2014, IMO will start discontinuing support for all third-party instant messaging networks.
Con A bit more difficult to set up than similar solutions
The process of generating and/or acquiring certificates can be time-consuming and a bit more complex than setting up a username/password authentication that's found in other clients.
Similarly, setting up a server that includes configuring user permission system requires advanced technical knowledge.
Con Relatively poor voice quality
While Mumble's voice quality is fine, and you can understand what's being said, there is a noticeable difference between it and many other platforms.
Con Disconnect issues
Can have occasions of disconnect or users kept getting booted.