I am starting with Facebook as I am always impressed with all the project they have open sourced till date and how other companies including fossBytes uses some of these technologies. Facebook uses, maintains, and contributes to a significant number of major projects- in areas as diverse as native mobile tools, big data systems, client-side web libraries, backend runtimes and infrastructure, and through the Open Compute Project, server and storage hardware. Facebook’s GitHub account alone, now has more than 90 repos comprising over 40,000 commits and that have collectively been forked 15,000 times.
Facebook contribution to open source can be largely categorized into Mobile, Web, Back-end and Infrastructure. Top open source projects made in these categories are: