Horizontal layout with drop-down sub-menus in desktop width
Ideally a vertical concertina in mobile width
Touch-friendly - i.e. will show an expand/contract icon on touch screen devices or on all devices
Cross-browser friendly (including ie7)
It seems to me that these are pretty normal requirements, used on many sites, but it's quite difficult to find a suitable plug-in library.
The closest I've found have been flexnav which is buggy in internet explorer and smartmenus which has a funny approach to the top level links for touch devices (the top level menu items trigger drop down, then turn into standard links after the sub-menu is displayed. There's no collapse button so a person can't minimise an expanded menu manually).
Does anyone know of a suitable script library? What do commercial sites use - does each developer write their own or do they rely on paid-for libraries?