FontMapper is a free/open source font texture generator for game developers written in Java. It allows you to turn a font you have installed to a PNG texture of tightly packed glyphs, accompanied by a text file describing the glyphs' properties and texture coordinates. You can read these in a game to render fonts. FontMapper supports Unicode (although only the Basic Multilingual Plane, i.e. the 16-bit codepoints), and each glyph can have its own size, i.e. fonts are not necessarily monospaced.
Currently, FontMapper is command-line only, although there might be a GUI frontend in future.