Open Freely is an ambitious program that not only allows you to open and view more than 100 common formats, but can also open and edit some of these.
Format support is much as you'd expect. So the program can open OpenOffice and Office documents, PDF files and many regular document formats (RTF and XML, for instance).
Open Freely also works as a media player, able to play all the main video and audio formats (even SWF). It supports many archive formats (7z, ZIP, RAR, GZ, TAR, TGZ, JAR, DEB and more). And the program can open images, source code files, Google Earth KML files, even many executable formats.
Unusually, you can also edit some of these, so in theory at least you can open a Word .DOCX file without Word, make changes and save the results.
Not bad at all for a free tool, then - but there are problems.
Format support isn't always the best. We opened some Word documents and quickly found a few that Open Freely wouldn't display properly. We're not sure that we would trust the program to edit and save anything complex.
Also, when you install Open Freely it installs the K-Lite Codec Pack (Standard), too. This may not always be a problem, but if you've got your codecs set up just the way you like then you may not appreciate someone silently installing such a huge update.