Earlier this year, more than 2600 MS-DOS classics were playable in your browser via the Internet Archive. Now such games can be embedded into tweets, effectively allowing you to play DOS games in Twitter.
Classic games like Lemmings, Wolf 3D or Prince of Persia can now be seen as playable games inside people's tweets. The Internet Archive's goal is to create a, well, archive of items for people to access in the years to come. There are some concerns about these games being offered for free, and some titles - for example Duke Nukem 3D - have already been removed since they are still available for sale. One would expect others to face a similar fate, especially now when developers could be reminded of their old game via Twitter.
So, if you are having an argument with someone on the internet, it's nice to know you can always play some Street Fighter while waiting for that reply. They're all here, and all free, complete with chiptune sound-effects.