At my company, we adore O365, but we looked at Yammer honestly didn't understand what it was for, and didn't understand why you'd want a social network at work for any company size, small or big.
What we actually needed? A logged chat that isn't inherently tied to any other service (ie, if O365 problems arise, we can discuss it, etc etc), and we tried HipChat early on and swapped it out for Slack.
Re: comments about Slack desktop clients being webviews... Slack seems to be much faster and use less RAM than Hipchat's desktop client which was also a webview. I can't tell Slack's desktop client is a webview tbh, even though I know it's one.
Slack also has that killer feature of knowing when you're not at your desktop and can interact with your phone in certain ways based on that knowledge.
What we actually needed? A logged chat that isn't inherently tied to any other service (ie, if O365 problems arise, we can discuss it, etc etc), and we tried HipChat early on and swapped it out for Slack.
Re: comments about Slack desktop clients being webviews... Slack seems to be much faster and use less RAM than Hipchat's desktop client which was also a webview. I can't tell Slack's desktop client is a webview tbh, even though I know it's one.
Slack also has that killer feature of knowing when you're not at your desktop and can interact with your phone in certain ways based on that knowledge.