You can use GeoGebra to find the orthocenter and altitudes of a triangle. 
     GeoGebra Instruction 1
Algebra     View     and         Graphics     View     under         View     in         Menu.         Polygon Graphics     View     where         you         want         the         vertices         of         the         triangle         to         be.         Finally,         complete         the         triangle         by         clicking         on         the         point         that         you         started         with.         Perpendicular     Line Intersect