An institution as enterprising as it is musically audacious, ICE brings back one of its most populist initiatives this week: OpenICE, a three-night series of free concerts. The opening set on Jan 29 brings works by Christian Wolff and John Zorn, in addition to a collaborative piece that features two ensemble members (the pianist Cory Smyth and trumpter Peter Evans). On Jan 30, an ensemble that includes flutist Claire Chase plays a set of recent compositions by George Lewis, Pauline Oliveros and Zorn. The final set on Jan 31 brings more items from Oliveros and Zorn, as well as a piece by the improvisatory team ExclusiveOr. Reservations are encouraged and can be made online at iceorg.org.