Open Office/Libre Office are basically the same thing, I don’t even know what the reason was for the split.
Butthurt in the program team.
Someone wanted something called “x” and it got called “d” instead.
Nerdraaaaage in the program room!
At least, that is a fairly likely scenario.
O-O was originally "Star Office" -- supported by Sun. When Sun was bought by Oracle, they forked Libre Office off, because the developers didn't want to deal with a proprietary system (like Oracle has done in the past with other things).
Also, O-O had gotten massively bloated by 2011. The Document Foundation folks went back and re-engineered the code to get rid of the bloat (when they came out with v3.5).
As it stands, Oracle dropped Open Office and it was picked up by Apache. I haven't messed with Open Office for a couple of years, but I read that the Apache team went and fixed O-O quite a bit since taking it over (but don't know that first hand).