The gcd command computes the integer greatest common divisor of a and b.  

$\mathrm{MapleTA}:-\mathrm{Builtin}:-\gcd \left(12\,15\right)$

$3$

The MapleTA[Builtin][gcd] command was introduced in Maple 18.

For more information on Maple 18 changes, see Updates in Maple 18.