When comparing IMO vs Rocket.Chat, the Slant community recommends Rocket.Chat for most people. In the question“What is the best team chat software?” Rocket.Chat is ranked 9th while IMO is ranked 20th. The most important reason people chose Rocket.Chat is:
Rocket.Chat is available for free. It's licensed under the MIT license with source code available on [GitHub](https://github.com/RocketChat/Rocket.Chat).
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 Free and open source
Rocket.Chat is available for free. It's licensed under the MIT license with source code available on GitHub.
Pro Native apps for all major desktop and mobile platforms
Rocket.Chat has native apps for macOS, Windows, Linux, iOS and Android.
Pro Supports a wide variety of authentication methods
In addition to the usual email / username + password combination, Rocket.Chat supports authenticating via Facebook, Github, Gitlab, Google, Linkedin, Meteor and Twitter accounts.
Pro Understands markdown better than Slack does.
Links work properly, for instance, with square brackets followed by parentheses.
Pro Very active and helpful community
Pro Video conferencing support
Rocket.Chat supports video calls.
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 Developer support is non-existent
Can't even create a clean Ubuntu VM with a working developer install. Unresolved dependencies; fails to build. Docs are terrible; actual devs don't respond to questions; error messages are near-opaque. DO NOT RECOMMEND.
Con Web client loses images
In chat rooms with images, before very long, images start to become empty boxes. Useless to pass around visual information
Con No theme customization
Con No chat audit for enterprise
Con Poor security implementations / protocols
Con iOS app is poorly made
The iOS application is not native, being just a browser container. This means that the UX is quite poor, slow, buttons unresponsive. At this moment they do not provide a decent experience.
Con Android app is poorly made
The Android application is just a badly wrapped web-view which does not perform well and has no form of offline caching whatsoever.
Con Privacy settings are absent
Privacy settings for the server are absent, for instance, you don't have the ability to disable registrations, there's no way to control access to the chat.
Con Features not available out of the box
Con No web browser support
Con Email required for registration
Con No way to block new registrations
Without the ability to disable registrations, there's no way to control access to the chat.