ATX, MicroATX, FlexATX, BTX, and NLX.
AT,ATX.NLX.btx
Atx, at and btx.
The five most popular categories of form factors used for motherboards are as follows: ATX MicroATX FlexATX BTX NLX In that order.
ATX, AT, BTX March, 12, 2010, the AT is kind of outdated, the most common now days is the ATX, MicroATX, BTX, and NLX.