I use LibreOffice on my work laptop (RHEL6) and have not had a problem. Where I really could use a replacement product is Visio as I do a lot of network and data center diagrams.
Have you looked into Pencil? It's primarily intended for wireframing mobile UIs and Web pages, but it also has stencils for flowcharts, and it's possible to download others, apparently.
That said, I was hoping to use it to sketch database ER diagrams, but was disappointed that it didn't have a stencil for that, at least not out of the box.