FontForge 
FontForge is a free (libre) font editor for Windows, Mac OS X and GNU+Linux. Use it to create, edit and convert fonts in OpenType, TrueType, UFO, CID-keyed, Multiple Master, and many other formats.
fontforge.org — homepage
designwithfontforge.com — font creation manual
INSTALL.md — developer instructions to build from source
.travis.yml — a list of installation dependencies
CONTRIBUTING.md — contributing guidelines