Mouse over macros.

[Ughmahedhurtz]

Note that "mouseover" macros and targets _cannot_ be passed on to your alts. It only works on the WoW window that has the active mouse cursor. (Caveat: yes, it can work under certain other configurations but that is a advanced topic best left for later, IMO.)

so thats a no-go on the /cast [target=main-mouseover] Spell?

That will only work on your main. It cannot propagate to alts. E.g.: "/cast [target=focusmouseover] spell" will not work as your alts cannot see your mouseover target.