alt Hacker NewsI wouldn't describe it as improved necessarily, but successfully integrated. This happened many times - youtube by google for example. Facebook acquisitions are pretty successful too (not looking if it was good for humanity, just from business perspective).
Some companies like Amazon buy companies and let them run almost independently - IMDB for example, Zappos, Twitch, Whole Foods, Zoox, Audible.
Android was also an acquistion by Google, run relatively separately, and it grew into something huge