Four Leaf Studios (or 4LS, for short) is the group that developed and released Katawa Shoujo. After a doujin released in 2000 by Raita Honjou came to light, Four Leaf Studios began work on the visual novel based on a bonus page at the end of the one-shot.
Four Leaf Studios was made by frequenters of 4chan's /a/ board. Since discovering the bonus page (circa 2007), the members put a lot of time and effort into making the game into what it is today, finally releasing the finished product in January 2012.
Four Leaf Studios offers the full game and the demo (which was translated to several other languages) of Katawa Shoujo, as well as the soundtrack and other media for download at http://www.katawa-shoujo.com/. It is licensed under Creative Commons BY-NC-ND License , thus being free of charge.
A list of members of 4LS and their involvement in the making of Katawa Shoujo can be found here.