Use one of the many peer-to-peer file control systems like hg, git or even fossil. It's the obvious way to do it:

• no central server
• secure
• backed up

<em> and <strong> have always been a part of HTML. The idea is that you are tagging structure, not layout. Text should be emphasized, or made to look strong. <b> and <i> are layout tags, which say to use a bold font or italicized font.

<em> and <strong> are preferred since CSS 1, because best practices say you should separate presentation/layout from structure. The former should only be in CSS, while the latter are in the HTML itself.

Qt's collection classes are API compatible with STL. So I would argue that it plays nicely already. I prefer Qt containers to STL containers because Qt's classes have been optimized. STL has some issues with performance.