I work for Red Hat, we do it all the time. We often acquire closed source companies and then release the software as open-source, while continuing to offer it.

I believe the most recent example was Stackrox, open sourced March 31st. The "productized" version is Red Hat Advanced Cluster Security. https://www.stackrox.io/blog/open-source-stackrox-is-now-ava...

Blender 3D might be one of the more well-known success stories in that regard. Godot game engine also perhaps? Gotta be more'n a few others as well, I'm sure. Those are just two that instantly come to mind for me (being a couple of my favorites that were both closed source at one time in their history and have gone on to massive and continual success since their open sourcing).

The web framework Remix was closed source and available only to license purchasers for about a year, until they announced their seed funding in October of last year: https://remix.run/blog/seed-funding-for-remix#open-source

The Canvas LMS: https://github.com/instructure/canvas-lms

Canvas was open source from the start. Schools have always been able to run their own instance, but most just pay Instructure to do it.

It wasn't open source at the beginning. (I know, I was there.) We open-sourced it early on, but it started as closed-source software.