Road cranks typically have two chainrings mounted on a 130 mm (or 135 mm) bolt circle diameter (BCD) with 5 bolts and the most common gearing is 53T/39T. A road triple has the same outer BCD and a 74 mm BCD for the inner (granny) chainring and are usually geared 52/42/30 or 50/39/30. The smallest 130mm BCD chainring possible is 38T and the smallest 74 mm BCD chainring is 24T

"Compact" road cranks have a 110 mm BCD and are most commonly geared 50/34 and the smallest chainring that will fit this BCD is 33T.

Current MTB cranksets have smaller BCDs for both the outer two and granny chainrings and commonly use only 4 fastening bolts. Typical chainring sets are the 44/32/22 you mentioned.

Older MTB cranks had 110/74 mm BCDs and were geared something like 46/34/24 but these are uncommon now. Some "Trekking" (i.e. touring) cranks still use these BCDs and similar gearing but often with a 48T large chainring.