When comparing Gitter.im vs IMO, the Slant community recommends Gitter.im for most people. In the question“What is the best team chat software?” Gitter.im is ranked 11th while IMO is ranked 14th. The most important reason people chose Gitter.im is:
Integrations for Trello, Jenkins, Travis CI, Heroku, Sentry, BitBucket, HuBoard, Logentries, Pagerduty & Sprintly are available.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Has many developer-friendly integrations
Integrations for Trello, Jenkins, Travis CI, Heroku, Sentry, BitBucket, HuBoard, Logentries, Pagerduty & Sprintly are available.
Pro Unlimited public and private rooms for free
Pro Has full Markdown support
Pro Has an IRC bridge
Pro Has apps for OSX, iOS and Chrome
Pro Has a Windows 8 app
Unofficial app for Gitter.im is currently available.
Pro Open source
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
Cons
Con Centralized
Con Apps / UX limited in functionality and can be buggy
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.