Brunswick Karma Urethane, Columbia Classic U2.
Several other companies have had them recently, but most hardly sold and have been discontinued. The market is just too tiny for most companies to continue to market them.
Balls, like the Brunswick Slingshot, and Roto-Grip Shout, are barely above the level of most urethanes. Pearl versions of these super mild cored balls, like the Ascent Pearl and Scream and Tropical Breeze have resin-like, stronger backends unless you're speed dominant. (Speed dominant bowlers see much less backend form these pearls than bowlers who are speed and rev matched.) So they're not really 1 step, but 2 steps above urethanes in ball reaction.