Linux is a kernel for GNU, which is a collection of apps that go back to the 50's, and most were open source (at least in practice) from the start. Over time some got reimplemented to preserve system compatibility, because of idiotic software patents and copyrights. That's why you can today use the same POSIX standard on Android, MacOS, Windows, your router or the university supercomputer. Compatibility isn't the same as cloning, unless your definition is very different from mine.
And if you saw how much Linux has diverged from the original Unix kernel philosophy (just look at the shitstorm surrounding systemd), you'd never call it a clone.
Clonezilla cloning Norton Ghost
Why Norton Ghost specifically? Hard drives have allowed partitioning back to at least the beginning of the FAT format, and copying your data from one location to another is one of the most basic operations you think of. Maybe it's not a bad idea to have tools to work with those open standards like FAT or BTRFS, which is why such tools go back decades.
Oh hey, maybe with a system tool like that, the important part is the stability and reliability which come from... Long term maintenance.
ReactOS cloning Windows NT
1) Again this is about reimplementation of system interfaces to make them compatible, not cloning
2) Yea do we want to break those closed source de facto standards like Windows and Adobe, or not? This is how you do it. Reimplement system calls, make software compatible. Wine is the same idea. This isn't cloning, by any definition. This is making a different kind of hammer for the same nails.
OpenOffice / LibreOffice cloning Microsoft Office
LibreOffice started way back as Star Office, which launched in 1985. That's years before MS Office.
Btw every major MS Office program was either acquired from somewhere else, or cloned. Go to Wikipedia and just read how Word, Excel, Powerpoint or Outlook started. Or DOS or Internet Explorer. Microsoft has always been about theft and intimidation. To point out that anything was cloned *from* them is hilarious, because you can be sure they stole it first.
GNU Octave cloning MATLAB, Mattermost cloning Slack
Ok I don't know much about these. But MATLAB is a bit of an anomaly. Most people that use programs/languages like these already make their own tools, which is why pretty much everything math- or science-oriented is open source and has started at some university or other. Then stuff gets shared and developed further. It's not surprising that people make tools compatible with some closed source outliers. Yea, again, that's how open source works.
GIMP cloning Adobe Photoshop in the 90s. etc.
Have you seen early GIMP? How can you say with a straight face that it's a Photoshop clone? People were bitching about the UI for like 15 years until they introduced the single-window UI.
And why take Photoshop as a benchmark? GIMP started in 1999, when there were still a million different competing graphics editors, because they had all started from the same painting programs on graphical workstations or home computers like the Amiga. These programs come and go. Adobe got into the monopolistic position in the same way as MS: by acquiring competing programs and either killing them, or merging them into their own suite.
Many projects start out as clones, then drift.
(...)
Blender is another ironic example, because they (finally) recently changed the UI to be much more consistent with Industry de facto standards. Rightly so, in my book.
Blender? An even worse example than Gimp. While most software of the same type have a lot of commonalities, Blender was like something made for aliens. How is this a clone?
And so which is it? Do open source programs *start* as clones and then drift, or do they start as something completely different and eventually maybe adopt UI similar to others? Those are very different claims.
The truth is, open source very rarely starts as a clone, because most projects start as little hobby projects that serve some particular need, or just because the programmer is learning, and eventually the project grows. That's exactly the opposite of cloning.
It's the software corporations that do the copying, because they can pay people to do the boring 1:1 cloning work which most programmers otherwise don't want to do, and maybe even more importantly, can pay the lawyers. Only very large, popular FOSS projects eventually get around to do some "cloning" like in terms of UI, when there's enough contributors so that some want to do such work, or if some organisation pays for it.
Otherwise, FOSS projects tend to resist consolidation the most. Look at the different desktop environments like Gnome/Unity, KDE, XFCE, that still keep their respective philosophies after 20+ years even if they occasionally stumble or reinvent themselves. Because FOSS has much less need for chasing trends, or for selling you the new shiny trinket.