Polymail - This one is a lot like Twobird but with a lot more features. It's a different type of email client. It's really cool, but the Windows version is just a web app. It's available on iOS as well. Source: over 2 years ago

Tools like Gather Town to encourage more ad hoc group interaction. One team I led used this tool daily for nearly a year, and the frequency and quality of our interactions were on par with an in-person office. - Source: dev.to / 10 months ago

Well, after some more googling I found a good candidate: gather.town if anyone is interested. Source: about 1 year ago

Our Guides will host live sessions throughout the April 28-30th weekend in our custom http://gather.town space to spark connections and learning among global participants. You'll form diverse teams, uncover shared goals, and explore a wide range of issues through the lens of Complexity! Source: about 1 year ago

I'm really digging gather.town for this. Our team has it set up & the ad-hoc "meetings" have gone up tremendously. You can choose to engage or not but it seems to be way more informal than slack for a quick sync, which is a gigantic strength imo. Source: over 1 year ago

As mentioned above by @yowzas648 you should check out https://gather.town We started using it this week with my team and it is game changing, it does exactly what you just described. Source: over 1 year ago