I assume from "these days" that you mean Gates, not Rockefeller.
Microsoft wrote some software that was, I would argue, overall an improvement on the software against which it competed. So Microsoft did some good. However, in the process of extracting value, they actively - and, in my opinion, often unethically - suppressed the efforts of those with whom they competed. I don't pretend to be very knowledgeable on the exact value of these positive and negative effects, but I think it's pretty clear that all of the above effects more or less amounted making a bunch of computer nerds like us a little richer, or a little poorer. Not necessarily in money, but in power... like the power to track business expenses cheaply (which Microsoft enhanced, with Excel), or the power to collaborate on making productive software for ourselves and share it freely with the world (which Microsoft harmed, see the Halloween Documents, or other conspiracy evidence of your choice).
For the most part, this only affects a few dozen million humans, and even interpreted broadly it affects perhaps 10% of humanity. And the effects are small; for almost all of the affected, life gets less than 1% better or 1% worse, due to Microsoft existing. I mean, that's bigger than most companies, but.
I'm less able to give clear magnitudes of the impact of the Bill and Melinda Gates Foundation. My understanding, though, is that they're playing a significant role in the attempts to eradicate polio. Frankly, you can inflict Windows95 on me for the next 50 years, if that's what it takes to save one person from polio. Suppose that it turns out that polio is eradicated, and the B&MGF is due 1% of the credit for that; wouldn't this be more valuable than all the harm ever done by MS, past and future? And then there's their malaria-eradication efforts, their money spent on education, their money spent on sanitation, etc etc.
Bill Gates seems to have stolen a very manageable amount of our first-world wealth, burned a good fraction of in an engine of inefficiency (for example, Ballmer got some money too), and given most of the rest of it where it could do the most good (modulo a small fraction kept for himself, to indulge in fabulous luxury). As far as I can tell, although it astounds and confounds me, Bill Gates is Robin Hood. wtf.