It was developed by the same core team that created Plan 9, and Limbo is the evolution of Alef, that Rob Pike wasn't happy to have to drop for Plan 9 3rd edition.

https://en.wikipedia.org/wiki/Alef_(programming_language)

> Alef appeared in the first and second editions of Plan 9, but was abandoned during development of the third edition.[1][2] Rob Pike later explained Alef's demise by pointing to its lack of automatic memory management, despite Pike's and other people's urging Winterbottom to add garbage collection to the language;[3]...

> The Limbo programming language can be considered a direct successor of Alef and is the most commonly used language in the Inferno operating system.

https://en.wikipedia.org/wiki/Inferno_(operating_system)

> Inferno was based on the experience gained with Plan 9 from Bell Labs, and the further research of Bell Labs into operating systems, languages, on-the-fly compilers, graphics, security, networking and portability.

For some strange reason many stop at the middle station, instead of going all the way to the end.