Cambridge River Fest, art and dance party from 9 a.m. to 11 p.m. in Central Square. Free.

This Cambridge Arts Council event celebrates a 35th anniversary that takes place away from the Charles River, thanks to construction, but promises a 9 a.m. to 7 p.m. experience otherwise the same as its 200,000 visitors have come to expect: jazz, folk, roots and world music performances; dance; art demonstrations and family art-making activities; and more than 150 specialty food purveyors, crafters and artisans showing and selling their wares. Information is here and a PDF of transportation detour routes is here.

Right next door to River Fest are art installations by Project MUM and the Firefly Arts Collective in University Park at 38 Sidney St. The collectives looked for creative and original art that encourages people to interact, participate and collaborate. (That fits the mission of Project MUM, which specializes in reclaiming underused public spaces.) This event – a sculpture garden from noon to 6 p.m. and a dance party with glow toys from 6 to 11 p.m. – has a suggested donation of $10.

Somerville Food Truck Festival with art carts from 11 a.m. to 4 p.m. Saturday at Assembly Row, 300 Grand Union Blvd., Somerville. Entry is $5 (cash only if you’re paying at the gate), or free for children 12 and under.

This first Somerville Food Truck Festival also launches the second season of Assembled: The Handmade Arts Market at Assembly Row and include New England Etsy artisans and food trucks, a beer tent, specialty food vendors, live music, sampling tents and children’s activities. Some of the participating trucks include: The Bacon Truck; The Latin Spoon; Bon Me; Maine’ly Lobstah; Cameo Macaron; Moyzilla yakitori and dumpling kitchen; Captain Marden’s Cod Squad; The Pasta Pot; Frozen Hoagies ice cream sandwiches; Roxy’s Grilled Cheese; Gabi’s Smoke Shack; Sweet Tomatoes; and Happy Taco.

Under the Influence of Fluxus opening reception from 4 to 6 p.m. at Mobius, 55 Norfolk St., Central Square. Free.

If you like your art punchy, funny and a bit weird, Reed Altemus has curated an exhibition for you as guest artist in residence at the Mobius art gallery through June 11. He has hand-selected artists from the neofluxus scene – that is, like the dada-inspired fluxus artists but neo-er – working in various media, including visual poetry, performance scores, boxes and such, and he extended an “open mail art invitation” to the mail art network for works that would fit through a mail slot. The opening of his “Under the Influence of Fluxus” show with accompanying performance is Saturday, followed by additional gallery hours from 1 to 5 p.m. Sunday and Tuesday and a closing reception from 6 to 8 p.m. June 11. Information is here.

Roller derby doubleheader at 4 p.m. Saturday, with games starting at 5 and 7 p.m. at Simoni Ice Rink, 155 Gore St. Tickets are $16 for adults, or $12 for students with valid ID; $5 for kids 6 to 17; and free for kids under 6.

Tickets include admission to the 5 p.m. matchup between the Boston B Party and Ohio Gang Green and 7 p.m. game pitting the Boston Massacre against the Ohio All-Stars – as well as to an after party with the Boston Derby Dames at the Massasoit Elks Lodge, 55 Bishop Allen Drive, Central Square, where there will be food trucks serving. Information is here.

A Prisoner* comedy show at Comicazi, 407 Highland Ave., Davis Square, Somerville. Tickets are $8 in advance online and $10 at the door.

As a BBC television show, “The Prisoner” lasted only 17 episodes in 1967-68, but the impact of this quintessential counterculture oddity has never waned. It’s inspired novels, comic books, games, theater productions, music videos (and the bands that make them), an art and music festival, a 2009 remake and now a paranoid night of comedy and thinly veiled look at local-scene skullduggery by Kevin Harrington, creator of Geek Comedy Night.

Fortunately, you don’t need a debriefing on the comedy politics to enjoy the comedy of Rick Canavan, Matt Chaves, Chris Coxen, Mark Gallagher, Wes Hazard, Nick Ortolani, Anthony Scibelli (and Tom Majkut as The Manager).