FontForge - Free (libre) font editor for Windows, Mac OS X and GNU+Linux
Microsoft Font Maker - Use your pen to create a custom font based on the nuances of your own handwriting.
BirdFont - Birdfont is a free font editor which lets you create vector graphics and export TTF, OTF, EOT and...
Scanahand - Scanahand makes it easy to create Windows Truetype fonts from your handwriting.
FontStruct - FontStruct. Build, Share, Download Fonts
FontCreator - This professional font editor allows you to create and edit TrueType and OpenType fonts.