Nepal is the only country with a non-rectangular civil flag, but the state flag of Denmark, Norway and Iceland are also non-rectangular. Here, flags at Christiansborg, the Danish seat of parliament.
The "split" flag is also used as war flag and naval ensign. Sweden and Finland also have non-rectangular war flags/naval ensigns, but with three teeth.
While not a state flag, multiple counties in Poland use flags that are made out of a coat of arms in a rectangle and stripes to the side that are shaped like a quarter-circle, trapezoid or a triangle. For example: