The purpose of the foundation is to ensure "Kotlin's development and distribution as free software, meaning that it is able to be freely copied, modified, and redistributed, including modifications to the official versions."
The next fastest growing language by the number of contributors is the Microsoft-maintained TypeScript, which grew 1.9 times over the past year.
This was followed by Microsoft's PowerShell and Rust, which has its roots in Firefox maker Mozilla.
Also rapidly growing is the cross-platform tool, CMake, the Google-created language Go, and Python, which is also one of the most popular languages among developers.
Filling out the top 10 fastest-growing languages on GitHub were Groovy, and IBM's SQLPL.
Microsoft remains the most active open-source contributor on GitHub with 7,700 employees contributing to its projects. Google had 5,500 contributors to open source, RedHat had 3,300, and UC Berkeley had 2,700.
The top-10 programming languages on GitHub have been fairly stable over the past three years, with the exception of TypeScript and Ruby.
TypeScript rose from 10th place last year to seventh spot in 2018. Ruby meanwhile has dropped from 5th in 2015 to 10th today.