This hasn't been updated in a couple of years and there are no instructions but it still works fine on my Dual 2.3 PPC G5 with Tiger 10.4.3. There are some limitations to be aware of however:

X Font does NOT recognize Postscript/Printer fonts (LWFN) and it will beep and do nothing if you try. It WILL recognize TrueType (Mac and Windows), Screen Fonts (FFIL) and OpenType (OTF).

X Font could use an upgrade to include preferences like adjusting the default character appearance (it is set at "ABC...123..") since most graphic and web artists will find this app useful. Plus a way to view the complete character map would be welcome. But this is free from the developer and it fits an important niche for those of us who have a plethora of fonts.