You could try looking at iplay4e, or Master Plan. Beyond that the .monster file is an XML file with a pretty strictly defined structure. I don't know if its possible to get a copy of the XSD schema for it, unfortunately WOTC didn't supply even a PI in the XML to give a hint where to find that. Even without it you COULD in principle build an XSLT transform to render the file in HTML (pretty easy, if you don't mind learning XSLT), or for a bit more advanced application you could probably generate pdf, stuff the data into an SQL table, or at least a CSV that you could suck into a spreadsheet and crunch into something fun to play with. Its all kinda going to be mostly up to you, and if that sort of thing isn't your cup of tea, well I don't know what to tell you. With 4e being out to pasture there's very little interest in building more tools for it. WotC was never highly supportive of the concept anyway, as the lack of a schema illustrates.