Mirr.io and Craft Prototype do have their similarities. It would probably be a good idea for me to do a comparison post at some point. Especially with the latest release of Craft.
In quick summary, Mirr.io was carefully designed to remove all barriers in getting your prototype working and shared. It has a live preview window on desktop and updates live on as many connected devices as you like (all through a single local url). With the new Craft, you are required to manually sync with the InVision ecosystem to view your prototype. But of course, this has its benefits like user comments, and project management.
Mirr.io aims to focus on the designer’s flow when working in Sketch. Keeping you designing and thinking in Sketch without hopping between other services.
Craft has a few more transitions which we will make sure we cover in the next releases (pop, flow etc). Mirr.io has support for headers and footers and different device sizes, which Craft Prototype has now dropped :|
We didn’t feel it necessary to draw connection lines between artboards as the live preview does a great job of showing you the real thing.
Framer we see as very different as it allows you to code your prototype, which can be very powerful indeed. We stayed away from exposing any code to the designer as there are great tools out there for this, which probably ends in building a real app in something like Swift or JS.
Mirr.io is in early stages, we’re excited and have some big plans for improving it over the coming months. I’d love to hear your feedback and please let me know if I’m mistaken on any of these points I’ve mentioned, it’s hard to be unbiased when it’s your own product :)