The Hidden Palace recently finished uploading their collection of 900+ video game prototypes to the Internet Archive. The Hidden Palace is a digital preservation community which has been collecting games since 2006, documenting their discoveries on their website.
The games in this collections span 4 decades! A lot of these have never seen the light of day, but now you can enjoy all of them from the comfort of your browser!
The collection is available at https://archive.org/details/hiddenpalace. So go on and dive into gaming history!
