This type of file is Unix Compressed File. This is an standard file format supported by many programs. This compression format is used to compress or "pack" files on Unix servers to save disk space; incorporates a simple compression algorithm that has been mostly replaced by GNUzip compression (which creates (.GZ files)).
File can be decompressed on a Unix machine by typing uncompress filename, where "filename" is the name of the file you want to decompress.
There is a lot of programs listed below for uncompressing/openning this type of file: