If you own the Samsung Galaxy S3 and you have been waiting for the arrival of Nougat you will be happy to hear that there is a custom ROM by the name of Android 7.1.0 This is based around Android Nougat and it comes with CM14.1.
Before you go ahead and install Android 7.1 Nougat on the Samsung Galaxy S3 you should make a backup of data. You also have to enable USB debugging and the handset must be unlocked, rooted and have TWRP installed. It should also have at least 60% battery life left.
To install Android 7.1 Nougat on your Samsung Galaxy S3 you will need the AICP Android 7.1 firmware saved on your computer and GApps.
Connect your Samsung Galaxy S3 to the computer and then copy the zip file to the SD card on your PC.
Turn off the device and boot into recovery by holding the Volume Up, Home and Power buttons.
Make a Nandroid backup of the OS and wipe the data from CWM or TWRP menu and choose wipe data/factory reset and then wipe cache partition and wipe dalvik cache.
Choose to install zip from sdcard and find the ROM you installed on the SD card and then confirm the process.
Go back to the main recovery menu and then reboot the Samsung Galaxy S3 and you should now be able to enjoy your new ROM. Bear in mind that the first boot may be longer than others.