Been using this more and more. It's not as powerful or feature rich as other prototyping tools but everything that is currently implemented is really smooth and well thought out. I like that it has a good balance of interaction stuff but also drawing tools so that I can build simple UI directly in it instead of having to design elsewhere and upload.

Here's a little demo prototype I made while exploring the tool

Woop, thanks for posting Karolis. I'm one of the designers at Atomic. Happy to answer any questions anyone has here.