We happily use Skylight at Product Hunt - especially since they've added their memory allocation stats it beats New Relic for most use cases. And its just so much more delightful to use :)
+1 super useful. I don't think it completely replaces New Relic yet. But the interface is much easier to use & memory allocation stats have been really helpful for us.
pganalyze
PlanetScale Boost
Delphi
INK'A
Moodelizer