Guster, the Tufts-bred band that’s celebrating its 25th anniversary, treated fans to a series of secret shows over the weekend, culminating with one at the Burren in Davis Square Sunday night. The gig, which kicked off after midnight, featured band members Adam Gardner, Luke Reynolds , Brian Rosenworcel, and Ryan Miller playing a set of other people’s songs, including “Miss You’’ and “Beast of Burden’’ by the Rolling Stones, “Dreams’’ by Fleetwood Mac, the Violent Femmes’ “Blister in the Sun,’’ and “Bang a Gong’’ by T. Rex. Guster was joined onstage by some Boston buddies, including Dave Schneider of the LeeVees, Tony Goddess of Papas Fritas, and Samantha Goddess of Jenny Dee & the Deelinquents, among others.