The open source office suite Libre Office gained support for exporting Epub files yesterday in its 6.0 release.
LO Writer exports PDF, of course, but now also Epub:
New filters for exporting Writer documents to ePub and importing QuarkXPress files have also been added, together with an improved filter for importing EMF+ (Enhanced Metafile Format Plus) files as used by Microsoft Office documents. Some improvements have also been added to the ODF export filter, making it easier for other ODF readers to display visuals.
Before this update your only option was to either export a DOC file and make the Epub ebook elsewhere or use an extension like Writer2Epub (which never worked very well for me).
Generally I made PDFs in Libre Office, not Epub, but then again I usually worked with non-fiction content like office documents and business paperwork.
P.S. Here are 14 other apps and online services that will help you make ebooks.