Sorry - lack of sleep. Are you talking about creating font sprites for construct 2.
All my font sprites are .png
Or you can individually create your own fonts in gimp/photoshop.
Edit: Give Your Fonts Mono as discussed above is nice tool. You can generate your font sprites with whatever tool. Open your font graphic in photoshop and apply style to it - there are 1000's of free styles, you will never have to create your own - trust me.
And I always save as .png