Proto.io
Information
(2)
$ 288
Other Info
Free
Yes
Offline
But prototypes can be viewed offline with native apps
Pen Tool
No pen tool
Collaboration
Simultaneous editing
Comments
Comments are supported
Handoff
Handoff not supported
Artboards
Multiple artboards can exist on a page
Symbols
No symbols
3D Transform
Can't skew or edit perspective
Responsive
No responsive resizing
Prototyping
Native prototyping