A staple of the jam-band scene, progressive bluegrass multi-instrumentalist Keller Williams is a refreshing oddball in a scene dominated by sub-Grateful Dead noodling and Dave Matthews-styled white-bread world funk. Williams plays well with others — The Travelin’ McCourys (The Del McCoury Band with Williams subbing for Del) are bluegrass masters, and trancey tribalists The Rhythm Devils successfully teamed Williams with the Dead’s rhythm section — but he is most effective as a techno-lysergic, one-man band. Improvising on his custom-made 10-string guitar, Williams builds layers of loops and doubles back on them like a snake swallowing its tail. A virtuoso on a host of instruments, Williams graces his improvisational, upbeat and benignly weird songs with an affable tenor and slightly sophomoric humor. Williams has a theater background, and his act is as much performance art as concert. Onstage, Williams is a nonstop blur, hopping from one piece of gear to the next. True, his humor never cuts as deep as Loudon Wainwright’s, and his surrealism can’t stir the soul like Robyn Hitchcock’s, but when Williams turns a meandering Dead opus into a direct and heartfelt ballad, you know you’re in the presence of a rare and unusual talent.