Flock Alternatives for iPhone

Slack is a cloud-based team collaboration tool.

Discord is a freeware proprietary VoIP application designed for gaming communities.

Glip is fully searchable, real-time group chat; video chat, task management, file sharing app.

Mattermost is an open source, private cloud Slack-alternative, Workplace messaging for web, PCs and phones. MIT-licensed.

Rocket.Chat free open source chat solution.

Bitrix24 is a free (for small businesses) social enterprise platform.

Voxeet is VoIP web conferencing software that uses 3D high definition voice technology to produce immersive sound.

Whaller allows teams and organizations to create their own internal social networks, meaning no adverts and no data exploitation.

TribeScale is an All-in-One platform to coordinate your team around what really matters - communication, goals, decisions, tasks and results.

Grape is an REST-like API framework for Ruby. It's designed to run on Rack or complement existing web application frameworks such as Rails and Sinatra by providing a simple DSL to easily develop RESTful APIs.

Zulip is a chat and collaborative software.

Dialog Messenger is a handy and feature-rich enterprise multi-device messenger available for server or cloud.