Gear diffs use gears for its differential action where ball diff's use balls. Open gear diffs aren't exactly adjustable. Sealed gear diffs are adjusted via diff oil. Ball diffs are adjusted via adjusting nut.
Other 'diffs' you can use are the one-way and the spool. The one way freewheels off power and locks up on power. The spool is always locked so the inner and outer axles always spin at the same speed.

Speaking of ball diffs. Is there a difference between the Manta ray diff and the TA03 diff? Does either one offer any sort of advantage over the other?