(W2X) is an all-round converter from odt to EPUB and a part of the writer2latex
family. It is meant to be used as a graphical extension integrated either in LibreOffice or OpenOffice. It's open-source (LGPL) and multi-platform like LibreOffice.
There is a French support thread on this forum.
Current version is 1.2. Coming version 1.4 (in beta stage) will support HTML 5 and allow the use of inline SVG images for vector graphics (clipart, drawings, charts).