You can now challenge anybody to an unranked game in correspondence mode. It looks like this - http://steamcommunity.com/sharedfiles/filedetails/?id=317164491 There is a limit of one game vs any particular person at a given time, so players you are already playing will have a grey color and won't be selectable.

There is also a resolution select dialog where you can specify a resolution at launch, or play in windowed mode.