The YF-23 was developed by Northrop (the same people who brought
you the B-2 stealth bomber) to compete with Lockheed's YF-22 (Now
F-22 Raptor) to be a multirole, air-superiority stealth
fighter
Unfortunately, it lost, so don't expect to be seeing production
versions.
As far as stealth fighters is concerned, Singapore is involved in
the F-35 JSF program, which I hope will replace the F-16s we have
today.