OpenOffice was acquired by Oracle recently when they bought Sun Microsystesm and have not embraced the open source philosophy in the opinion of the greater open office community. So, since the code is open source, several in the non-Oracle community decided to "rescue" the project from the same fate as Opensolaris. Libre Office is based on OO code 3.3 and GO-OO.
http://news.cnet.com/8301-30685_3-20014478-264.html