A UFO file is a file saved in the Unified Font Object (UFO) format. It contains data about a font, which includes the format version, creator, glyph layers, kerning information, images, and metadata.
UFO file open in Glyphs 2.4
You can create UFO files to store a font using Glyphs or RoboFont, which are font editors for macOS. You can also open and edit UFO files using Glyphs and RoboFont in macOS, or FontForge, which is available for Windows, macOS, and Linux.
UFO files are actually archives that store numerous files, which contain the font data. The files that can be found in a UFO file include .PLIST, .GLIF, .FEA, and .PNG files.
The first version of the UFO format was originally published in 2004 but is rarely used anymore. The second version was published in 2009 and is the most common version used. The third version was published in 2012 but is not as widely adopted as the second version. The format was developed and is maintained by Tal Leming, Justin van Rossum, and Erik van Blokland.