...there's a site for that.
I just found out about SimplyTest.me today, and it allows you to, well, simply test any Drupal.org-hosted module, theme, or distribution in seconds.
No longer do you need to spin up (or maintain) a live website locally (which usually takes an extra minute or two—at least) just to check out a module or make sure a theme or distribution fits your needs before using it on a live or development site.
Instead of simply getting a screen shot or trying a theme on a demo site, you get a full Drupal website set up and configured with the module/theme/distro (as well as it's dependencies), so you can play with it to your heart's content (for 30 minutes if you don't have an account on the site, an hour if you do).
According to the site's Q&A page, Drupal 6, 7, and 8 are all supported—even with sandbox projects! You can read more about the architecture and service implementation on the simplytest.me project page on Drupal.org.
Check it out, and thank Patrick Drotleff and all the sponsors (who help provide the hosting) for the hard work on this awesome tool!
[Update: There's also a great post on the Comm Press Blog about how you can test patches quickly and easily using Simply Test.me: Everyone can test patches. Really! simplytest.me to the rescue.]