"Thus my qualification "well known"."
So that, to you, means "i don't know anyone who used them"?
Because that's a pretty small definition of "well known".
For reference:
Inside the VCS community, they were very well known.
Graydon also went on to start Rust, of course.
Outside of that, even to corporations I dealt with (i was working on SVN at the time), plenty knew it existed, a few evaluated it.
" But both of these were experimental and extremely slow at the time git was designed."
I feel like this is just you trying to say "well, they never would have worked anyway".
DARCS was slow and couldn't be fixed, monotone was actually not that bad, and could be made very fast if necessary.
Monotone was slow precisely because it cared about integrity. If you made git care about integrity and security in the same way ... it would be just as slow!
Saying they were "experimental" is silly.
Monotone was self hosting and nobody had found data corruption or other issues in quite a while (IE > 1 year), AFAIK. This is much better than git was for a long time. To put this in perspective, i converted the gcc repository (hundreds of thousands of revisions, in fact, many more than the kernel at the time, and history going back to 1983) to monotone, and
1. the conversion worked with no issues
2. Speed was fine in most cases. If i worked hard, i could find issues, but ....
git was beyond experimental at the time it was designed (IE data loss and repeated crashes).
But it's design is essentially that of monotone in a different container and with slightly different goals.
(IE they precisely gave up the integrity part that monotone verified and cared about, and people are now complaining about).
In truth, if Linus had cared about cryptographic security, he probably would have just stuck with monotone and rewritten parts of it.
But he didn't, so he gave that up in the name of speed.
Which is fine, but let's not pretend that Linus somehow has a monopoly on design, or even was the first to design a VCS that was like git.
Any of the distributed VCSen could have beaten git. They just didn't care about the tradeoffs that git was making (IE non-portability in favor of speed), and honestly, it's pretty obvious git would have been laughed out of existence if it hadn't been supported by someone so popular to so many people.
In fact, it was laughed out of existence, the past N times people had devised VCSen that favored speed over portability.
Git is interesting as an example of how good marketing with the right figures sometimes leads to winning in the marketplace for long enough that you can fix the rest of your serious issues (IE everyone else had the OS/2 problem). Even more interesting is that everyone else backfills history to make it seem like it was the best and clearly the right set of tradeoffs from the start. It wasn't. It may not even be now!
It's like any other system.
Please don't try to backfill history here. I was there, as were many others.