Twist focuses on topic-specific threads within channels, rather than lumping all activity into a single channel. You won't risk distracting from an important project by posting about the upcoming company party, and the whole concept avoids the sense of urgency that comes with live discussions. The service still has real-time conversations, but you have to start them as direct messages -- they're not the default.
This might also be your ideal option if you don't like dealing with pings when you're off the clock. There's a "time off" mode (shown above) that silences alerts for a set period and makes it patently clear that you're on that long-sought vacation. You can also specify your regular schedule to avoid late-night notifications.
As a brand-new offering, it doesn't have the sheer amount of platform tie-ins as Slack or its counterparts (Todoist and GitHub are two of the larger examples). And this won't work as well if you absolutely need a large, anything-goes live chat to get things done. The price is right, however: it's free if you don't mind losing old messages and documents, and $5 per user per month if you want a permanent record. That's a good deal compared to the roughly $7 per person an employer pays for standard Slack access. Will it make established rivals quake in fear? Probably not, but it could carve out a niche at companies where always-on chat may do more harm than good.