When comparing Flowdock vs Mumble, the Slant community recommends Flowdock for most people. In the question“What is the best team chat software?” Flowdock is ranked 4th while Mumble is ranked 10th. The most important reason people chose Flowdock is:
An easy & simple interface to filter chat discussion into separate threads.
Specs
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Pros

Pro Threaded discussions
An easy & simple interface to filter chat discussion into separate threads.
Pro Drag and drop file sharing
Files can be dragged and dropped in to the flow dock screen for upload.
Pro Multi-platform
Browser Based, as well as:
- iPhone and iPad App
- Android App
- Mac OS X App
Pro Stored chat history
Content and discussions are stored forever.
Pro Smart pastes & code syntax highlighting
Pro Private chat option
Able to speak privately/talk head-to-head.
Pro Notification system
A specific user or everyone in the channel can be notified via @user or @everyone respectively.
Pro A full developer API
Flowdock API allows developers the freedom to create custom integrations.
Pro Create and assign PRs from Flowdock
You can interact with Github directly from Flowdock to create PRs.
Pro Free for teams of five, non-profits and students
Pro Data exports
Back up conversations and files fully at any time.
Pro Add Tools
On top of our 50+ custom integrations, easily integrate any tool that sends emails or generates RSS feeds, as well as having the option to build a custom integration with Flowdock's API
Pro Status updating
Allows co-workers to know what you’re up to "/status I'm busy today!"
Pro Google Apps Integration
Google Apps get a Flowdock link to the Apps tool-bar and won't have to separately manage users
Pro Typo Fix-ups
Pro Able to host users external to your team
When working with stakeholders (clients or partners) you can add organizations to manage internal privacy
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 Free and open-source server software
The server software Murmur is licensed under a free and open-source BSD-style license.
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 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.
Pro Push-to-Talk
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 Free to download and use as a client
Mumble is completely free, even hosting your own server.
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 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 Sub-channels
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 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.
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 Portable version on PortableApps
Pro Server can be put on alternative firmware wireless routers
Cons
Con Proprietary (non-free/libre)
Con No self-hosting available
If you are worried about third-parties getting access to your data you should consider self-hosting. With self-hosting you are in control over where your data is stored, who has access to it. You will also not be vulnerable to exploits of a third-party provider.
Con Buggy android app
Google sign up didn't work, then after going to the website to do the sign up, the invite team members screen was broken.
Con Free only for small teams, non-profits or students
Unless it's used by a team of less than five people, a non-profit or students, Flowdock will cost $3/mo per person.
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 Disconnect issues
Can have occasions of disconnect or users keep getting booted.
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.
