CSP (Cryptographic Service Provider)
Officially deprecated by Microsoft, it is the mechanism intended to talk to Windows CryptoAPIs. Therefore, you can never talk about a CSP for Mac, or a CSP for Linux.
KSP (Key Storage Provider)
It replaces CSP and implements the new generation of Windows crypoAPI, called CNG (CryptoNextGen).
The problem with KSP is that it is only supported in applications that use a recent version of .NET and, therefore, right now it is a compatibility problem because there are more applications that have fallen “behind” than those that already support it.
Viafirma Fortress Desktop = CSP + KSP
Alternatives for Mac and Linux
Desktop application that actually implements an interface to PKCS#11, exactly like the smart card, token and HSM drivers do.