[dodobirdlord]

Google’s standard employment contract gives it default ownership of basically any software produced by an employee if it has anything to do with the employee’s job or Google’s business, which means basically everything. But it’s also very easy for an employee at Google to open-source software. The consequence of this is that frequently when a Google employee has a side project that they want to share with the world it will end up released as a Google open-source project under a permissive license.

[reikonomusha]

I think that it’s also that Google employs Common Lisp programmers and maintains Common Lisp code.