FontForge - Free (libre) font editor for Windows, Mac OS X and GNU+Linux
NexusFont - Choose and manage your fonts with Nexus Font.
BirdFont - Birdfont is a free font editor which lets you create vector graphics and export TTF, OTF, EOT and...
Font Viewer - Font Viewer is an application which does exactly that - it views fonts!
Glyphs - Make everything from dingbat webfonts to full-fledged text typefaces in the most Mac-like font...
Font Manager - Simple font management for GTK+ desktop environments