Semaphr
· All-in-one kill switch for your mobile apps. With semaphr, you can force users to update to the latest version of your mobile apps, encourage app updates, or alert them of any issues with the app.
Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window Semaphr-1.0.4.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.