That's why, in Windows systems, I install a link to Vern Buerg's ancient list.com in my SendTo folder. Open the file with list, hit alt-H (I think) and look at a nice hex/ascii dump. Then you at least have a chance of making sense of what's inside. Sometimes binaries will contain copyright notices.
Failing that, I ask Google, which produced a couple of credible hits on "obs file extension" without the quotes.
Mike Halloran
Pembroke Pines, FL, USA