Classic Reload is a website that lets you play Dos, Commodore 64 and Sega Genesis/MegaDrive games in your browser, so that you can just play right away and not have to worry about fiddling with settings.
You can play some of my favourites, such as: Moraff’s World, Donald Duck’s Playground, Hugo’s House of Horrors, Cosmo’s Cosmic Adventure, Dracula in London, Crosscountry Canada, Mario Brothers VGA, Mavis Beacon Teaches Typing, and ETC!