ChatGrape vs Slack

Take your conversations with you, wherever you go. Stay connected to your colleagues and don't miss a discussion anymore - the ChatGrape mobile apps for iOS and Android will keep you updated and let you join the conversation easily, no matter where you are. Reference all data from your external services from within ChatGrape right as you type - with an autocomplete that knows your business.
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:

2015 - Enterprise group chat ChatGrape launches publicly. Slack keeps calm

ChatGrape, the enterprise and team messaging app that pitches itself as a more intelligent Slack or HipChat, has launched publicly. Along with offering the standard enterprise and team messaging features, akin to the hugely popular and well-funded Slack, ChatGrape has built what is essentially a search engine that indexes various tools and services that you connect the app to. These include Box, DropBox, Google Drive, GitHub, BitBucket, Jira and others. Typing # directly into a chat triggers ChatGrape’s smart autocomplete — now called the ‘Grape Browser’ — enabling you to quickly look up and link to/reference files or data from any supported third-party service. The startup also offers an API, making it possible for companies to integrate their own internal data into the chat app. And to coincide with today’s public launch, ChatGrape has given its look-up functionality a further boost by letting you search and add data from public external sources, not just those to which you explicitly connect the app, such as GIF sharing app and YouTube.