Flems is a playground for web development. It's ideal for prototyping ideas & sharing working front-end code examples.
Unlike other playgrounds, Flems doesn't require a connection to the server after page load: all the code you write in a Flems is computed in the browser and saved as a compressed string in the URL. The only thing you need a connection for is downloading extra dependencies. This means you can type away without needing to 'save' a Flems and the URL in the location bar will always be a shareable link to exactly what you're seeing.
Comments and Reviews
The benefit of Flems for me is that I can write my HTML/CSS/JavaScript code and test it at the same time as the results appear instantly, and this option is enabled by default (you can switch it off if you wish).
Unfortunately, no way to change the font size.
It might not be a full HTML editor with code snippets and such, but it has syntax highlighting, code completion and code folding, which make it a quite useful tool.
A unique URL is generated, so that you can keep working on your code at a later date. No registration required!