An "App Store" is not a requirement for having a sandboxed environment.

Consider these examples:

1. Your web browser. 2. Java and .NET programs can be run in different trust-modes only allowing certain functions from the standard library, and obviously disallowing external libraries then. This is mostly used on servers to isolate websites on the same server today but if given a better user interface could have been used to secure desktop programs. 3. User permission levels in operating systems