Building on the Napo framework, Clavitudo is a container app that allows you to play various supported instrumental sample sets by MIDI keyboards connected to your iOS or macOS device.
The instruments have to be installed by the user. For more information, please consult the app support page https://polaron.de/Clavitudo/ . For a quick start, read https://polaron.de/Clavitudo/Manual/Quickstart/ .
The 0.x versions of Clavitudo are free. From version 1.0 on it is planned to be subscription-based.