Third members explained?

What's the difference in "open" "trac lock posi" "true trac" "detroit locker posi" ? if there are any other variations you can offer up a definition or link for reading, i'm sure someone else would appreciate this also.....

/////some links now, if these are different from anything else, info helps us all

differential's explained(overview) : http://www.youtube.com/watch?v=F40ZBDAG8-o
true-trac : http://www.youtube.com/watch?v=lZmsY2YvVsc
detroit locker : http://www.youtube.com/watch?v=FYBOoljH-qE
i think this is open : http://www.youtube.com/watch?v=iBLE0_Sjqw4&NR=1