Gulliver's Travels. Swift's satire set to original music. Presented by the Cambridge Ensemble at the Old Cambridge baptist church, 1151 Mass. Ave., through February 28. Performances Thursday through Saturday at 8 p.m. Tickets $3.50.

Equus. a fine production of Peter Shaffer's powerful exploration of madness. Also the longest-running show in Boston this year--it's run has been extended umpteen times already, but it probably won't be extended again, so get tickets while you can. At the Wilbur Theatre, 252 Tremont St., through February 21. Performances every evening at 8 p.m., matinees Wednesday and Saturday at 2 p.m.

Hamlet. Shakespeare MIT-style. Presented by the MIT Community Players February 20-22 and 26-28, at MIT Kresge Auditorium Little Theatre, February 20-22 and 26-28, at 8 p.m. Tickets $3.00.

The Alchemist. The classic by Shakespeare's rival Ben Jonson. Presented by the MIT Dramashop at MIT Kresge Auditorium Little Theatre, February 13 and 14, at 8 p.m. Tickets $2.50.

The Apple Tree. A Sheldon Harnick-Jerry Bok adaptation of short stories by Mark Twain, Frank ("The Lady and the Tiger") Stockton and Jules Feiffer, performed in a cabaret setting with pre- and post-curtain entertainment. Presented by the Hubs Pub Theatre at the Ramada Inn, 1234 Soldier's Field Road. Performances Tuesday, Friday and Saturday, at 8 p.m., through March 2. Tickets $3.50-$4.50.

The Haunted Host. A comedy about gay love in Greenwich Village and a revival of the virgin effort by Robert Patrick, whose Kennedy's Children previewed here successfully this fall. At the New Theatre, 12 Holyoke St., in Harvard Square. Performances Tuesday through Friday at 8:30 p.m., Sunday at 3 and 7:30 p.m.

The Importance of Being Earnest. Oscar Wilde's marvelously farcical parody of Victorian love. At the Lyric Stage, 565 Boylston St., in Copley Square, through March 28. Performances Friday, Saturday and Sunday evenings at 8 p.m., Sunday matinees at 3 p.m.

Zalmen or The Madness of God. Or it's not easy to be a Jew in post-Stalinist Russia. At the Shubert Theatre, 265 Tremont St., February 17-29. Performances Tuesday through Saturday evenings at 8 p.m., matinees Thursday and Saturday at 2 p.m. and Sunday at 3 p.m.