JOdin3 Alternatives
JOdin3 is described as 'open source Odin for Windows, Mac, Linux, can be used from your browser too. This tool which can flash your Samsung device with software' and is a Modding app. There are three alternatives to JOdin3 for Windows, Android, Linux and Mac. The best alternative is Heimdall, which is both free and Open Source. Other great apps like JOdin3 are Odin and Mobile ODIN.
Heimdall is a cross-platform open-source tool suite used to flash firmware (aka ROMs) onto Samsung mobile devices.
Discontinued
Heimdall has not received updates since 2017 and does not support new versions of GNU/Linux distributions.
Odin is a utility software developed and used internally by Samsung which can be used to flash a Custom Recovery firmware image (as opposed to the Stock recovery firmware image) to a Samsung Android device. It is also used as a way of unbricking an Android device.
Mobile ODIN is the on-device firmware flasher of choice. Just throw those firmware files on your (internal or external) SD card, start Mobile ODIN and flash away.
Discontinued
New updates have stopped, replaced by free app Flashfire. See update release date (May 1, 2014) in Play Store listing.