"Smart Card Middleware" usually means a set of libraries that allows integrating the smart card in third party applications. But the question is which exactly are the libraries supplyed by a smart card middleware? The schema below shows the "Big Picture":
On Microsoft OSs we will find the Cryptographic Service Provider (CSP) and the minidriver (a sort of mini CPS). On Microsoft OSs we will find the PKCS#11 module too for applications that doesn't use the CSP, such as Firefox, Thunderbird, etc.
On Linux, MacOS, iOS and Android we will find the PKCS#11 interface that applications and apps must call to communicate with the smart card.
Finally on MaxOS we will find the tokend interface too, even if it has been deprecated by Apple.