I have used Keynote on the mac for most of my prototyping needs. I help teams come up with a really cheap prototype as part of the design thinking experience and we have used keynote for both desktop and mobile prototypes. It supports clickable actions and some amount of animation with magic move.

Here is a great video from WWDC 2014 where they talk about the how.
https://developer.apple.com/videos/play/wwdc2014/223/

If you need help, give me a call.

One of my favorite combinations is Sketch + Invision.

I develop the prototype with Sketch (sketchapp.com) then I import the prorotype to Invision (invisionapp.com), make it interactive/clickable, and share with all my testers to gather feedback/comments.

Let me know if you have further questions - I'd love to help!

- Ryan

Invision (https://www.invisionapp.com/) is definitely one of the best out there.
Pop (https://popapp.in/) is a good simple option.

There are plenty of other options as well. Depends more on what you are building. We can hop on a call and chat about it if you want.