CoreMIDI
Apple's MIDI layer in macOS and iOS, built into the operating system so keyboards and software find each other without third-party drivers.
On classic Mac OS, MIDI was handled by add-ons such as Opcode's OMS and Mark of the Unicorn's FreeMIDI, and which one you had decided which programs worked. Mac OS X made MIDI part of the system, alongside Core Audio: every application sees the same devices, can share them simultaneously, and can create virtual ports to pass MIDI between programs. Class-compliant USB keyboards just work, and the Audio MIDI Setup utility draws the whole rig as a map.
Mac OS X 10.4 added network MIDI, Apple's implementation of RTP-MIDI, and iOS 4.2 brought CoreMIDI to the iPad in 2010 – which goes a long way to explaining why the iPad became a serious instrument well before Android tablets did. Later releases added MIDI 2.0. Windows got nothing comparable until much later.