Trinket is a browser-based tool/app that lets users write, run and share their code right on the browser without a need to download, install any software and/or plugins.
I tried it for Python and works great. One of the drawbacks is it only supports limited amount languages. At this point it supports Python, Blocks, Html5, and GlowScript. Despite these limits, if you are learning Python, or use Python on regular basis, you may find this tool to be useful.
Another aspect I find very useful is that is education focused. First, tool itself is great if you are just starting out learning to programs and provides ability to test out various small codes from any device. In addition to that, they provide interactive tutorials, so the students can learn in an interactive way at they code.
While they have paid subscription plans, which are not too expensive, for average users it is completely free. Visit their website and see if Trinket is something you would be interested in.