To Mock Or Not To Mock...
When inspiration strikes, sometimes you have to record your ideas on whatever is handy. Back of an envelope, napkin, or even your hand. And if you are a developer, odds are you have done something like that with some aspect of web or software UI.
For something simple going from napkin to implementation is possible. But for anything more involved you usually want to mock up or wire-frame your ideas, either to flesh them out, or to communicate them to others.
Once upon a time this may have required a degree in Photoshop, but now there are many web-based tools providing the ability to mock out your interfaces and more.
Moqups
Moqups is a fairly full featured application which can handle UI wireframes or general diagramming. It has a lot of stencils, but on the free plan you are limited to 200 objects. It feels like the free plan is designed as an evaluation option, but you could certainly use it for a small project.
MockFlow
The free plan on MockFlow is a bit more capable, limited to a single project but no object restrictions. Otherwise the functionality is similar to many other diagramming tools. It does seem like there are more integrations and extra features that may make this a viable option if you decide to upgrade.
Wireframe.cc
This one is a bit different in that you don’t need an account to use it for free. Just visit the site and you are greeted with a new wireframe to work on. The tool is deliberately limited, keeping true to the wireframe concept rather than adding realistic stencils and the like.