I wrote about this on reddit only recently ...
Link to the discussion there
Copied in full to here:
So back when Sun maintained OpenOffice.org and sold StarOffice they had a Contributor License Agreement that required handing over ownership of patches to them so they could sell the closed source supported suite and license out to IBM for Symphony.
To get around this bureaucracy and to not sign over ownership for patches most distributions used go-oo.org (aka ooo-build) that was the source code of OpenOffice.org with a bunch of patches on top to help compatibility with MS Office and some other things that Sun could or did not want in the upstream oo.org code.
When Oracle bought Sun they left oo.org languishing with no maintenance for months. This was naturally unacceptable to the various linux distros and they didn't want to be beholden to Oracle's whims (for good reason given the state of the various projects that used to be with Sun). Due to this they got together and formed The Document Foundation and took the go-oo.org code (which was basically what this group used and collaborated on anyway) and forked it to LibreOffice.
Fast forward some more time and Oracle decide they don't want anything to do with OpenOffice.org after all and essentially (with IBM's help ... presumably so there would be a sort of maintained base for Symphony) dumped it on the Apache Software Foundation. As per their requirements it went through an incubation process and all the code was relicensed to the Apache Public License. This was months after LibreOffice had been created and worked on and most consider it a pretty petty move rather than giving the brand to TDF to work with.
From that point on it's pretty much been IBM driving Apache OpenOffice (as they renamed oo.org to) although they appear to have stopped caring about it mid to end last year. The amount of development work on AOO is minimal compared to LO and the number of active committers is in the teens (at best) for AOO compared to the hundreds for LO.
Due to the way the licensing works out LO can merge in any fixes (there were some in the early days, not many now as can be seen in the CVE issue I mentioned) but AOO cannot merge in work from LO.
The last release of AOO was August 2014 and if you go look at the changelogs from 3.4 (the first AOO release as opposed to oo.org IIRC... mostly rebranding) up to the 4.1.1 then you'll see there's been minimal work - mostly translations. Anything developed/fixed in AOO is either merged into LO or improved/obsoleted by other work. Compare these to the release notes for each LO release from the forking point of 3.3 and it really is quite significant - the heavy work on clean up and better build systems for LO lower the barrier to entry for LO contribution by the common person too.
The proposed AOO release of 4.1.2 is going forwards at the moment - driven mostly by only a few people Apache OpenOffice Dev mail archives.
To give an idea how bad this has got the no-interaction code execution as privileges of user bug by a special HWP file was announced publicly last April. It was fixed in LibreOffice the same month and users would have had the update notification and been protected. Anyone using Apache OpenOffice is still vulnerable and although there was a disclosure on the security part of the AOO site at the time, the workaround was to 'delete .dll/.so' ... not a release with a fix and unless anyone actively went to check up on this they would not have known the issue.
To add to this (if it's not enough already) AOO can still only read and not write docx/xlsx/pptx (OOXML) files produced by MS Office whereas LibreOffice can write these as well... and LO fixes a lot of layout bugs in the translation of the formats.
Finally don't be confused by the version number jumps and think significant progress has been made in AOO compared to the ancient OpenOffice.org... There have only been a few actual releases in this time under the Apache umbrella ... compare this to the release schedule of LibreOffice.
Okay that ended up being a lot more history and writing than I was planning on - I hope you see why AOO is slowly dying and why anyone sane and following along with the history will be using LibreOffice instead if they care about performance, compatibility or security.... and if you made it this far you earned yourself a cookie ;)