I grew several grassroots software projects in a 5-digit size company. The last had least 10-15 direct contributors and tens of others involved. It grew so large the CTO organized a summit to get the main IT organization along with everyone else involved on the same page and it came out as the "winner".

I did all this as an individual contributor. We called them "internal open development" and had developed an entire model around it. You can basically create "parallel" hierarchies within organizations. It's not that different from the "build something people want" idea, but it actually makes those people part of it.

There were several other projects like this.