FontForge - Free (libre) font editor for Windows, Mac OS X and GNU+Linux
BirdFont - Birdfont is a free font editor which lets you create vector graphics and export TTF, OTF, EOT and...
Glyphs - Make everything from dingbat webfonts to full-fledged text typefaces in the most Mac-like font...
FontLab VI - font creation and editing, including variable fonts and color fonts
FontStruct - FontStruct. Build, Share, Download Fonts
TruFont - TruFont is a font-editing application written with Python3, ufoLib, defcon and PyQt5.