37signals: Ruby on Rails, Basecamp (software), Web application, Illinois, Chief executive officer, Usability, Design, Writing, Open source, Software framework, Freemium, Paul Horowitz

37signals is a privately held web application company based in Chicago, Illinois, United States. The firm was co-founded in 1999 by CEO Jason Fried, Carlos Segura, and Ernest Kim as a web design company with a self-described focus on usability, simplicity, and clarity in design and writing. 37signals also produces a blog, Signal vs. Noise. Segura left in 2000 and Kim left in 2003, leaving Fried as the only remaining founder. Since mid 2004, 37signals has been primarily a developer and provider of business and personal productivity web applications. Its first application was Basecamp. This was followed by Ta-Da List, Backpack, Writeboard, Campfire and Highrise. 37signals was responsible for launching the open source web application framework software Ruby on Rails, which it uses in its own applications. The products have gained popularity using what has come to be known as a freemium business model. The company is named for the 37 radio telescope signals identified by astronomer Paul Horowitz as potential messages from extraterrestrial intelligence.