Free Viewer can help you view a really wide array of file formats. It not only supports opening text files, documents and archives, it goes far beyond that and lets you open different types of media files, such as audio, image and video files. An application like this may come in handy when you need to open a given file whose supporting application is not installed on your computer.
I do not think anyone would have difficulties using Free Viewer because there is practically nothing to do but to view the files. It has a modern interface with a tabbed ribbon that contextually changes according to the type of opened file. Also depending on the file, some quite simple editing functions are available.
The program is rather non-invasive as it will not substitute other program’s file associations. Instead, it will set itself to open extensions that are not associated to any other program. In addition, it lets you customize file associations at will. Although the program is completely free and will not bother you with any kind of adds, you should be cautious during installation or it will add a probably unwanted new bar to your web browser and change your default search engine.
In general, Free Viewer serves the purpose it was created for. Of course there are file types that are not supported, and that is logical, because a real universal viewer is just an ideal.