If you mean RGB SCART, some consoles are modifiable to output RGB but not all.  I think the Genesis is.  The NES is not without stealing some parts from a Playchoice.  Google usually knows if a given console has a simple mod.
If you just mean "something I can hook up to a SCART intput on a TV", SCART supports composite video.  Pretty much all consoles since the NES have had composite video output options.  Placing this on a SCART cable isn't hard, but it won't work with an arcade monitor.