Glip vs Slack

Plan, share, & organize work in real-time. Glip organizes your team’s work while you chat with your co-workers, and makes your conversations productive. All your projects, meetings and files live in the stream, so everyone is in the loop on what’s happening.
Slack brings all your communication together in one place. It's real-time messaging, archiving and search for modern teams. Create open channels for the projects, groups and topics that the whole team shares. Slack searches whole conversations, not just individual messages, so you can find what you’re looking for no matter who said what or when they said it. Slack free open-source (self-hosted) alternatives are: Mattermost, Rocket.Chat, Zulip
Face to face in the news:

2016 - Slack adds video calls to keep up with Glip

Collaboration messenger Slack is adding one more key feature - video calling. Group video calls, for those on paid tiers, can handle up to 15 people currently, Slack says. The new feature will be available first on Slack for Mac and Windows on desktop and Google Chrome in the next few days. Those on mobile will be able to join video calls but will experience them as audio only. Video calls in Slack will have an interesting add-on - emojis. A lot of people who use video and audio conferencing for calls with work colleagues will turn on the mute button so that their random coughs and sighs or other ambient noise will not interrupt the soliloquies of their coworkers. Now if they want to make quick responses to things they won’t have to fumble around for the unmute button: instead they can offer a thumbs up, or whatever is right for the moment.

2014 - Glip declares The End of task management to catch up with Slack

Glip is one of the new productivity tools that look more like social network, than task manager. According to Glip's philosophy: Task - is just another form of communication. Glip developers say: "If we could simply harness our conversations, the organization of work itself would be the organic result? You don't have to pray to the software gods for something that will help you manage your tasks any longer. It's time to get things done the natural way... Just be human. Just Glip". So, Glip allows easily convert conversations into tasks. And it's free, untill you reach 10,000 posts and 5GB of storage. Glip competitors include HipChat, Slack and Flowdock.