Take a look for yourself at http://copy.sh/v24/. There’s 4 OS images you can load directly from the page, including FreeBSD, Linux, FreeDOS and KolibriOS which is GUI based. You can also load your own ISO images to boot in the emulator. KolibriOS works fine so does FreeDOS, which even has some playable DOS games like Tetris and Snake which brought back memories of my MS-DOS days.
For experimental purposes only I also downloaded a Windows 3.1 ISO CD image off piratebay and tried to run it but it didn’t really work (I think the problem was with the image not being properly bootable rather than the emulator – after all Windows prior XP was first booting MS-DOS and then running Windows). I also attempted to load TinyCore Linux but I didn’t get far with that one either. TinyCore’s ISO is just under 15MB with GUI included. It took around 10 minutes to boot on an i7 laptop but never made it into the GUI.
Anyway if you don’t have the time to fiddle around you can view the following 5 min video I made running the emulator in Chrome: