Free Opener claims to open over 80 different file formats—anything from Microsoft Office documents and PDF files, to image, video and music files, with many more in between.

FreeFileViewer is another free universal file viewer software for Windows 10. You can view DOC, DOCX, PDF, TXT, XLS, XLSX, JPG, PNG, GIF, PSD, FLV, MP4, MOV, MPG, FLAC, MP3, OGG, WMA, BIN, CFG ...

Letter Opener isn't cheap, and the utility vs. cost ratio is dependent on how many winmail.dat files you deal with on a daily basis. Prices range from $29.95US for a single license, to $179.95US ...