From 1967’s Hair to 2015’s Hamilton, with A Chorus Line (1975) and much more in-between, the Public Theater is arguably the most influential theater company in America. This year the Public’s annual celebration will livestream free of charge to theater lovers around the globe, at eight P.M. E.S.T. The more than 30 alums who are on board to appear and perform is spectacular, and includes Antonio Banderas, Glenn Close, Elvis Costello, Claire Danes, Anne Hathaway, John Leguizamo, Audra McDonald, David Hyde Pierce, and Sting. The artistic honoree this year is Sam Waterston, whose 13 performances with the Public include title roles in Hamlet (1975) and King Lear (2011). The gala is hosted by the redhead from “Modern Family,” Jesse Tyler Ferguson (he too is a Public alum). A post-performance dance party streams live on YouTube. —L.J.