Is there any way to write a WinRt (Metro) app that will also work on Windows 7 and Vista?

Question

We can’t just leave our customers that are not able to upgrade to windows 8 for a long time in the larch. However there is demand for a “tablet”/”touch” versio

Answer 1

It is unlikely that we'll see Microsoft push the Metro-style application framework back to past releases due to the level of re-architecting that went into Windows 8.

Like Pavel said, if you kept your application from using as much of the WinRT libraries as possible, it is possible but then again, you're now building a regular web app.