Slack vs Symphony

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
Jumpstart team productivity. Everything you do is protected by Symphony’s unique end-to-end security. Enhance your messages with rich editing, images, tables and files. Hashtags, cashtags and mentions - never miss an important message with personalized filters. Secure access to your conversations on your desktop or on your iPhone.
Face to face in the news:

2017 - Slack now allows to add comments to particular message. Symphony keeps calm

Workplace communications tool Slack has introduced threaded comments. With threads, users can pop out of the chaos of an ongoing chat and pin bits of conversations off to the side that they can address on a more regular basis. Users can jump in and out of their existing threads much like they do channels and direct messages, and when they want to share new comments back into a chat stream, they can do so by hitting a small checkbox at the bottom of their new message. The threads are located in the panel that pops out on the right side of your screen that has additional tools and resources for your existing rooms and direct messages. Starting a thread is as simple as clicking on a button next to a message in a room, much like you would add a reaction, and then it peels off into a new conversation within the right panel.

2016 - Enterprise group chat Symphony adds voice, video and key app integrations. Slack is in panic

Symphony, the enterprise messaging app, is adding new voice, video and screen sharing features in the form of a new product called Symphony Meetings, and it is also launching the Symphony Webhooks API, giving companies the ability to create their own integrations with third-party apps alongside a list of apps that Symphony itself is integrating from Salesforce, Github, JIRA, Trello and Zapier. Unlike Slack, Microsoft’s Yammer, Hipchat Symphony is directing its own product not so much as a general enterprise app, but it takes some of the consumerization trend that helped form those other apps and is applying it specifically to the finance vertical.

2015 - Google invested in secure enterprise chat Symphony to keep up competition with Slack

Symphony, the secure cloud-based communications platform, has received a $100 million round from a list of investors that includes Google. Certainly, this is an interesting investment for Google. It’s not exactly a secret that Google has had trouble with social and Google + seems to be the forgotten step child these days. Google could be looking outwardly, and Symphony not only offers a secure communications tool that could help compete with Microsoft’s Skype/Lync, it also has some intriguing content tracking abilities, letting you follow hashtags and keywords both inside the system and in public social networks like Twitter that could be attractive to Google.