shasum has no output, why?
Tinkertool.app is just a folder. You need to run it on the actual app. Your command should be shasum -a 256 /Users/douglas/Desktop/TinkerTool.app/Contents/MacOS/Tinkertool

You can get to the actual app by right-clicking on Tinkertool.app and selecting "Show package contents" and navigating to the actual app.