RNAV is just a form of area navigation - it's been around since the 1970's the earliest crudest form of RNAV was with the VOR/DME
RNAV computers "VOR mover" (you might find these avionics, like the KNS-80 on some older aircraft)
In some aircraft, RNAV is implemented by the FMS. Most smaller general aviation aircraft don't have an FMS, so an appropriately certified GPS receiver alone does qualify as RNAV.
Our airline has FMS equipped CRJ-200's/700's but we're not authorized in our opspecs to fly RNAV(GPS) / RNAV(RNP) approaches, we still have to switch to green needles and fly instrument approaches using the old NAV receiver using ILS or VOR/VORDME.
However we are allowed to use the FMS to fly these new RNAV DPs that are starting to be implemented across the US in places like Las Vegas, Dallas, Atlanta.
At airports served by major air carriers, RNAV approaches are a kind of a waste because any ILS, even a Cat I ILS will have lower minimums than a RNAV approach, it's a no brainer to go with ILS - an ILS will just get you down lower.
The biggest beneficiary of RNAV approaches is general aviation (little Cessnas and corporate/business jets) who operate out of smaller airports that might not have spent the money to get an ILS installed. RNAV will probably have lower minimums than the non-precision VOR/NDB approaches.
There are newer RNAV approaches - Approaches with Vertical Guidance (APV) which provide vertical guidance - similiar to the glideslope of an ILS. You can tell those approaches from the older RNAV approaches by looking at the minimums criteria. You'll have LNAV minimums, LNAV/VNAV minimums, and LPV minimums. The LNAV minimums is like the LOC minimums of an ILS - you can use those minimums if your RNAV equipment isn't certified or is incapable of providing the vertical guidance, just like you can shoot an LOC only approach instead of a full ILS approach. The LNAV/VNAV and LPV minimums are available for you to use if you have the RNAV equipment which provides the vertical guidance.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.