Currently I've been using Invision, but curious if there's something out there that allows for simple animations as well.
It can do incredible complex, responsive interactions and is not cloud-hosted.
I've wondered this myself.
I played around with Marvel recently, since it allows for web prototypes. Sadly, there's no built-in animation feature. It does allow for the uploading of GIFs so if you wanted to demo micro-interactions within pages, you could try your hand at that.
Allows me to prototype faster, and putting my design from my PSD is easier then ever. Plus using custom masks are high importance.
I feel like it's easier to drive your user, then have them guess what works and what doesn't.
Can't forget video, what if you have a person that was removed from a green screen, in the background or a video?
Most of those online Prototype creators won't allow embedding video.