The navigator.standalone attribute has been in iOS since forever and has the nice semantics in that, as a boolean value, it distinguishes between installed web applications and those running in the regular browser tab.

It's slightly unfortunate that "standalone" will mean "installed" (as per the spec's definition), and there is also "display-mode: standalone", but I think that's ok.

What do folks here think? @dmurph, @aarongustafson, would love to hear your thoughts!

See also this webkit bug.