capstone

capstone    [Kap-stohn] 

noun.  a final touch, a crowning achievement 

"The flyby of Pluto by NASA’s New Horizons spacecraft is rightly celebrated as a triumph of human ingenuity, the capstone of a mission that unfolded nearly flawlessly."

"The acquisition of Nokia was considered as a capstone to Steven Ballmer's long tenure as Microsoft's CEO."

"Marriage equality was the capstone of this productive legislative session."