#UbuntuTouch was originally developed by Canonical as an alternative to Android & iOS. It shipped on some phones, such as the Meizu PRO 5, & a couple of tablets. It could also be flashed onto one's own device.
In early '17, Canonical restructured and dropped UT. After that, it was picked up by the @Ubports community, and they have been developing it since.
UT was originally based on 15.04, but since OTA 5, released by UBPorts, it's base has been updated to 16.04 LTS.