Mods, pretty please make this a sticky. Background Skip over this section if you just want to get up and running as quickly as possible. Normally when you download and run a Java program such as OpenRocket, it executes using the system JRE (Java Runtime Environment) installed on your machine. Unfortunately, different JRE versions (especially the newest ones starting with 1.9) do not always retain 100% compatibility. Or even if they're compatible in theory, various problems can crop up that cause your Java program to misbehave or crash. There are other annoyances as well, like you can't pin the OpenRocket JAR file to the dock on the Mac (at least, not in the app area where you'd want it), and on Windows OR doesn't behave well with high-DPI screens. A solution to all these problems is to use packaged versions of the application. These install like regular applications, and include their own JRE built in. This bundled JRE will remain completely separate from your system JRE, and will only be used by OR. Therefore you do not need to have Java installed on your machine. Over the course of several months, these packaged installers have resolved every single instance of user having trouble running OR. At least that I've heard about. The current version of OR is (still) 15.03; these packaged installers run the original OR code; nothing has been changed or modified here. Windows Click here for the installer. The file is hosted on Dropbox, but you don't have to register or anything. If you see this dialog: just click on "No thanks, continue to view" at the bottom and then click the "Download" button on the next screen. The application uses a standard installer, but it doesn't (at present) provide a shortcut on the desktop or the start menu. After installing, the actual executable file for the application is installed into your user/AppData/Local/OpenRocket folder. So you can go in there, right click the "OpenRocket.exe" file, and create a shortcut, pin it to the taskbar and/or pin it in the start menu, whatever. Mac Click here for the .dmg file. Again, this is on Dropbox; see above instructions to bypass the "register" dialog if you get it. This behaves like a typical application image: double click the downloaded file, and it will open up a window showing the OR icon and an alias to the "Applications" folder. Drag the OR icon onto the Applications folder icon and the app is installed there. Then run it from that folder, or use Launchpad, Spotlight, or whatever other application launcher you favor. Enjoy!