Preferred Internal Wiki Platform?

As a startup, we found that Google Drive was sufficient for maintaining things like policies and procedures. Then, we hired people. I'm leaning toward using an internal wiki as a way to organize divisions, departments, policies, procedures, etc. and am interested to hear where you all have had successes or failures.

What are your favorite platforms that accomplish this goal, whether paid or OSS?

Also, any pro tips on how to effectively organize and manage an internal wiki are appreciated.

Or is there a better solution for organizing a company's internal knowledge and resources than a wiki?