clickdummy lets you create click-through prototypes from screens you design in a tool like Sketch or Photoshop.
clickdummy is also a great way to easily integrate an image-based prototype into an HTML prototype.
I built clickdummy to have a simple tool to create click-through prototypes from screen designs especially for situation where third-party services are not an option, maybe due to legal reasons.
Usually I build my prototypes with Protostrap. Sometimes I am part of a team where pure HTML prototypes are not an option due to the team members' different skillsets. Having a prototyping tool that allows me to combine screen-based prototyping with the dynamic prototyping I am used to is a great way to collaborate.