I’ve been tempted to buy AudioSwift for Mac for this purpose, but I’ve also been able to meet the same need by connecting my Android phone to my Mac using the LK app for Android by Imaginando with the accompanying UBridge desktop app. This allows a variety of touchscreen interfaces, switching between a mixer, keyboard, chorder, and drum machine layout.
Connecting phone to laptop is a somewhat “brittle” and fidgety connection, so I’m about to get a Roli Block pad that can double as a drum pad, mixer, and sampler interface. It connects wirelessly to the computer or an iOS device via Bluetooth or USB.
I recently got the keyboard form factor and have been very happy with the portability, connectivity, and built in sounds, so I’m looking forward to adding the pad to my setup.