The SandboxIE website has been updated to declare that the application-isolation software will become open-source. Until then, the current owner, Sophos, has made all features of the current Sandboxie free for all users. Anyone can download it from the official website. Previously, the application was split into a full version, and a non-commercial version with some features disabled.
I used this software quite a bit when I was on Windows 7. They (reasonably) did not support Microsoft’s initial Windows 10 Insider Program, so I stopped using it in late 2014. The software is designed to wrap applications that can read untrusted data to contain the application if it gets exploited by malware in the data. While this can be very practical, I often used SandboxIE to create profiles of certain applications. For example, Notepad++ remembers the files that you had open in the previous session. When I worked on multiple websites at the same time, I would create a SandboxIE instance per project, so I could launch the program and be greeted by the correct file tabs.
If you’re interested, give it a try and report what sorts of problems you use it to solve.