Similiar to BMFont you get an image and a data file, there's a few formats, one in particular is CEGUI Font that includes an .imageset file that seems to be just an ordinary xml file.
Here's a piece of the beginning for a test font I made...
<?xml version="1.0" ?>
<Imageset Name="test font" Imagefile="test font.png" NativeHorzRes="800" NativeVertRes="600" AutoScaled="false">
<Image Name="0032" XPos="0" YPos="0" Width="0" Height="0" XOffset="0"/>
<Image Name="0033" XPos="2" YPos="2" Width="7" Height="15" XOffset="0"/>
<Image Name="0034" XPos="15" YPos="2" Width="8" Height="15" XOffset="0"/>
<Image Name="0035" XPos="28" YPos="2" Width="9" Height="15" XOffset="0" etc... />
There's also one "XNA Format" that also seems to be an XML file;
<?xml version="1.0" encoding="UTF-8" ?>
<font base="13" height="15" >
<bitmaps>
<bitmap id="0" name="test font.bmp" size="256x128" />
</bitmaps>
<glyphs>
<glyph ch="!" code="0021" bm="0" origin="2,2" size="7x15" aw="3" lsb="0" />
<glyph ch=""" code="0022" bm="0" origin="15,2" size="8x15" aw="4" lsb="0" />
<glyph ch="#" code="0023" bm="0" origin="28,2" size="9x15" aw="5" lsb="0" />
<glyph ch="$" code="0024" bm="0" origin="41,2" size="9x15" aw="5" lsb="0" />
<glyph ch="%" code="0025" bm="0" origin="54,2" size="12x15" aw="8" lsb="0" />
<glyph ch="&" code="0026" bm="0" origin="67,2" size="11x15" aw="6" lsb="0" />
<glyph ch="'" code="0027" bm="0" origin="80,2" size="6x15" aw="2" lsb="0" />
<glyph ch="(" code="0028" bm="0" origin="93,2" size="7x15" aw="3" lsb="0" etc... />
And lastly a format just called Font. It exports 1 .fnt file that isn't clear text so I don't know much about that particular one.
It's easy to try out if you have downloaded the program from the link I provided, no installation needed. The program starts up with a basic font ready to be exported; File > Export Font, then pick one of the options.