> GIF was, despite patents a dominating image format for a long time and PNG took quite a while to replace it.

Yes, and it caused quite some legal grief for many software vendors.

> If we look at video codecs "open" variants are quite a small part. Heavily patented MPEG dominates the space over webm etc.

We were talking about Open Source Software, not patents. There are lots of OSS codecs for the various MPEG formats.

> Windows still got a very successful proprietary API. (Or set of APIs)

Depends on what you call "successful". Sure, it's been in use, thanks to a quasi-monopoly. But I'm not aware of any other OS implementing the Windows APIs because they think it's a great set of APIs. There are some projects like "wine" that try to implement it to offer compatibility, and it took them many years to make it mostly work.

Would it have been better for society as a whole if Windows had implemented System V APIs instead of their own, proprietary APIs?

Monopolies are the other avenue to introduce new protocols and formats, but apart form that, OSS seems to be the main pathway to introduce them.

https://reactos.org/ implement some of the windows API

> Depends on what you call "successful".

Could you give a reasonably mainstream definition of “successful” that would exclude Windows?

GIF was fully open and free, before it wasn't. After it had established itself as a standard, was when Unisys and IBM started in with the patent they had on the compression algorithm. Note that GIF could have switched to a different compression format, but that would have had the same issue that PNG had in that new images wouldn't be compatible with existing viewers (and that was in the days before the concept of "evergreen" web browsers -- they didn't get automatic frequent updates).

And the other thing holding back the switch to PNG was that people weren't all that confident that there weren't any unknown patent landmines in that standard. You don't know until either one goes off (some patent troll convinces a court that a generically worded patent applies), or until enough time elapses (20 years) that all potential patents would have expired.

And Windows now has WSL to implement the open API, because it's so popular. And implements SSH and sudo, because they're so popular. Etc :)