XDA Senior Member piggZ has released a community port of Sailfish OS for the Xiaomi Redmi Note 4. The build is currently in alpha state so there are quite a few things either missing or broken at the moment.
The port is based on Lineage OS 13.1 and requires you already have an unlocked bootloader and custom recovery installed. The list of things that are currently working fine include calls, data, Wi-Fi, GPS, and Bluetooth. If you're looking to try something new on your Redmi Note 4, give it a shot. Be sure to check out all the instructions before you attempt to install it on your device.