Snap a photo of your idea sketch and make it interactive with Marvel.
Even better than the good idea, the whole thing is free and you can sync via Dropbox so your resources are all available everywhere your Dropbox folder resides.
If it turns out that you aren’t a designer or even particularly good at sketching your great idea, Marvel also has a Resources section where you can get free “kits” of graphics created by other people. So far they are mostly PSD, but there is a set of UI elements for Sketch if that’s more your speed.
I actually enjoyed using this; it let me illustrate an idea that was hard to communicate otherwise. Plus if you want to collaborate with someone remotely, you can embed your prototype in a web page to allow someone else to play with it.
This is a handy tool for anyone who has a need to create a lightweight version of an app idea and be able to share it with others easily, no coding required.