the Linux kernel
termIT supportprogramming
The operating-system kernel Linus Torvalds began in 1991 and which is now developed by thousands of contributors from competing companies - monolithic in architecture, released on a fixed cadence, with selected versions carrying years of long-term support.
Two properties explain its reach. Its licence forces distributors of modified kernels to publish their changes, which makes upstreaming cheaper than maintaining a private fork - so competitors cooperate out of self-interest. And its hardest rule is that userspace must not break: internal interfaces churn freely, but a program that ran yesterday must run tomorrow. Almost everything except the desktop runs on it - servers, phones, routers, cars, industrial controllers and every machine on the supercomputer top list.
Also known as: linux, mainline, vanilla kernel, lts kernel