An O.S. can be an operating system as well as this type of software like Firefox, GIMP & Thunderbird
[DOC] [TLE] The Top 50 Proprietary Programs that Drive You Crazy  and Their ... [PAR] Jan 22, 2013 ... Windows 10 to Ubuntu: This is Microsoft's operating system (OS), and even ... 
system, you can still use an open source browser like Mozilla's Firefox, an ....