It's called "Thief Font Converter", but the same font format is used in
System Shock 2. In fact, it goes all the way back to the original System
Shock game for DOS!

It takes a bitmap image of the outlined font glyphs and creates a font. Also, you can convert a font back to in image for editing. This latest update adds support for 8-bit grayscale fonts that have recently been added to the unofficial New Dark patch of the Dark Engine. The tool can read bitmaps in BMP, GIF, PNG, or PCX format at 8 and 24 bit depths.