Supported Platforms: iPhone, iPad, Android, Mac, Windows, Linux and Web-based solution.
Pricing: Free for unlimited users with no support for data export and $4/mo for Premium plans with all major features and priority support.
Pie
Pie is a great free app for team communications and collaborations. It is more of an augmented chat application that includes all the key features you would need in a full-fledged team communications application. Available on all major platforms and with an Apple Watch app lined up, Pie is a great Slack alternative if you are looking for a completely free tool.
Key Features: Chat and collaborate with co-workers directly, Perfectly syncs on whatever platform accessed, share files and import from different third-party file hosting services.
Choose reason:If all you need is a full-fledged chat application that would help your team collaborate better and boost their productivity, Pie is one great Slack alternative. Given that their are absolutely no restrictions, users or searching logs, Pie is definitely a great free alternative to Slack.
eXo Platform
eXo Platform is an excellent Enterprise-ready open source social platform for team communications to build their network upon. eXo platform offers a top-notch team communications platform that is completely customizable as per the necessities of the enterprises. With an open source social networking platform, eXo platform provides the ultimate team communications solution for a major enterprise.
Key Features: Cloud-ready, Customizable UI, Extensible APIs, Third-party integration, localization, productivity tools, social networking, content management and collaboration.
Choose reason:If your enterprise is in need of a highly structured, powerful and feature-rich team communications solution, eXo Platform is a great tool to build your internal communications around.
Supported Platforms: Cross-platform with mobile-ready Android and iOS apps.
Pricing: Self-hosted variants range from $1,200, $2,200, $4,000 to $8,000 for 25, 50, 100 and 250 users; Cloud-based variant is priced at $3/mo per user.
Yammer
Yammer is a great premium team communications solution that integrates all the key features of such an app and offers the reliability on top of it. Microsoft is now the parent company for this tool and that makes it even easier to integrate and collaborate easily with other Microsoft products. With a powerful context-based search feature and support for all major platforms, Yammer is a great team communications alternative to Slack.
Key Features: Discover content easily with powerful context-based search, Single Inbox to keep up with latest news and updates, Document collaborations and more.
Choose reason:Yammer is a great tool that offers premium team communication features that you would definitely wish to have on board. This tool is backed by millions in funding by the top venture capitals and eventually sold out to Microsoft for a hefty sum. This definitely makes Yammer a tool that people would definitely put their money into and you should too.
Supported Platforms: Cross-platform, Web app and all major mobile platforms like iOS, Android and Windows phone.
Pricing: Free for educational organizations, $3/mo per user for Enterprise standard plans and $5/mo per user for Businesses.