The browser should be all you need: the xml and xsl file. Alternatively, you can still ger v2.18 of the STIG Viewer as its still java-based (but no, not FOSS).
Personally, I use the browser. Then, if I want something I can add comments and such, I had a script which took the controls and put them into tiddlers for importing to a TiddlyWiki (though that was a few years ago).