“We’re stronger when we sing together,” read Pete Seeger’s quote over the entrance gates, and the Newport Folk Festival carried out that credo this past weekend, proving stronger than ever with wildly collaborative voices.

Marcus Mumford and Brandi Carlile

Maggie Rogers, Brandi Carlile and Chris Thile

Like a giddy summer camp for free-minded musicians and a roving audience along for the ride, the three-stage festival at harbor-side Fort Adams State Park was rife with largely spontaneous sit-ins. Jason Isbell brought out David Crosby to rock “Wooden Ships” and “Ohio” to cap Friday’s first day. Saturday’s “unannounced” headliner (speculated to be Neil Young — whose usual backup band Lukas Nelson and Promise of the Real played a very solid set earlier that afternoon — or perhaps Bruce Springsteen) instead turned out to be British folk-rock revivalists Mumford & Sons, who threw in covers from Radiohead’s “All I Need” to the Band’s “The Weight,” assisted by such guests as Brandi Carlile, Phoebe Bridgers, Maggie Rogers and the mighty Mavis Staples.

Valerie June

Brittany Howard and Mavis Staples

Sunday’s closing “A Change is Gonna Come” set – anchored by Jon Batiste and the Dap-Kings, and nodding to the 50^th anniversary of the civil rights era – reveled in many more guests. Carlile delivered Bob Dylan’s “The Times They Are A-Changin’” with the both-unbilled Rogers and Punch Brothers mandolin virtuoso Chris Thile, who added an offbeat duel with pianist Batiste. Lake Street Dive’s Rachael Price sang the hell out of the Sam Cooke song from the program’s title. Leon Bridges — another surprise guest – teamed with Gary Clark Jr. for “Ohio” (a subdued contrast to Friday’s version), then joined Thile and the Preservation Hall Jazz Band for “I’ll Fly Away.” Alabama Shakes’ Brittany Howard (there with her trio Bermuda Triangle) went toe-to-toe with gospel icon Staples for “Jesus on the Mainline.” And the whole cast – also including Valerie June, the Lone Bellow’s Brian Elmquist, Nicole Atkins, Bedouine, Caamp and the War and Treaty – spread across the stage as Batiste and Staples led a levitating romp through the Staple Singers’ “Freedom Highway.”

Margo Price

Even more cameos dotted the weekend. John Prine introduced rising country star Margo Price and returned for a duet of his song “In Spite of Ourselves.” Warren Haynes (Gov’t Mule, ex-Allman Brothers Band) sat in with Wilco’s Nels Cline for acoustic blues nuggets. Langhorne Slim and the Suffers’ Kam Franklin joined the Lone Bellow for the prayer meeting-like “Then Came the Morning.” Carlile came out for a tune with the theatrical Lucius (whose set included interpretive dancers acting like synchronized swimmers) and when the Berklee-schooled duo of Jess Wolfe and Holly Laessig began to sing, a smiling Carlile modestly shook her head and hands in awe.

Courtney Barnett and Jen Cloher

But Newport Folk wasn’t all about collaborations – and there was nothing wrong with Carlile’s pipes, especially during her own sterling set, which peaked when she followed a rendition of Joni Mitchell’s “A Case of You” with a Led Zeppelin-worthy charge through “Babe, I’m Gonna Leave You.” Carlile was among a contingent of Newport alumni who’d graduated from smaller stages to make their main-stage appearances count with extra verve. Those acts included the Lone Bellow (the versatile soul-roots rockers led by the preacher-like Zach Williams, Courtney Barnett (who rocked the main stage on Saturday, then served in the band of girlfriend Jen Cloher on the small Harbor stage on Sunday) and Margo Price. The same went for Jason Isbell, whose Friday headlining slot with his 400 Unit surged with songs of real-life details (he and fiddler wife Amanda Shires traded knowing glances during their co-written “Anxiety”) long before Crosby emerged.

Adam Weiner of Low Cut Connie

Tank and the Bangas

As curated by producer Jay Sweet, the festival also introduced vibrant new acts. Adam Weiner fronted Philly rock ‘n’ rollers Low Cut Connie in a Vegas-style jacket and medallion, channeling Jerry Lee Lewis and standing on his piano to exhort fans, paying homage to Tom Petty and Prince, and ripping his muscle T shirt to charge through the aisles of the Quad tent. New Orleans’ soul-funk sparkplugs Tank and the Bangas tore up the same stage behind wide-eyed singer Tarriona “Tank” Ball’s body-quaking dance moves. Delta Spirit’s Matthew Logan Vasquez found a rambunctious new vehicle in the roots-rock ensemble Glorietta. On the mellower side, Alabama Shakes’ Howard shared the spotlight with “best friends” Becca Mancari and Jesse Lafser in the more folky Bermuda Triangle. Tyler Childers and the deep-voiced Colter Wall honored traditional country. And Moses Sumney transfixed with finger-picked guitar and falsetto vocals that he electronically looped.

Stylistically, Newport Folk clearly mixed things, from the American blues of Ben Harper and harp veteran Charlie Musselwhite to the West African blues of Sidi Toure to the reggae of Toots & the Maytals. The Texas trio Khruangbin conjured atmospheric grooves from psychedelic soul and Thai funk. In a real departure for her, St. Vincent sang her arty electro-pop songs in a stripped-down cabaret format on the Quad stage, backed only by the piano of Thomas Bartlett while her guitarist uncle Tuck Andress, who played earlier with Tuck & Patti, watched side-stage. And Sunday morning kicked off perfectly with a choice between the gospel-driven husband-wife team the War and Treaty or the boisterous Preservation Hall band. Newport Folk’s only mismatch was Cheech and Chong. True, comedy’s a growing component at festivals nationally (even at Solid Sound and Boston Calling), but the stoner duo’s skits seemed like a change of pace that was out of place.

Shakey Graves

Of course people once said that about electric guitars at Newport, which – years beyond Dylan’s blasphemous transition – also reigned this past weekend, from Fantastic Negrito to Shakey Graves and especially Sturgill Simpson, who blasted past his country roots. But anybody who wondered what happened to Newport’s old troubadour spirit could have hit the coffeehouse-size Museum stage (usually after a long wait) or even the main Fort stage for Passenger, the solo vehicle of British singer/songwriter Mike Rosenberg. He promised misery and singalongs, had a brandishing style and wit akin to countryman Frank Turner, and offered a song about his dad’s grandparents who immigrated to New Jersey, noting that both our countries are “built on immigrants and long may that be the case.”

Yes, some artists made political statements on the Newport stage (Ben Harper dedicated “I Don’t Believe a Word You Say” to “the soon-to-be ex-president”). But the music mostly did the talking, even in Sunday’s “Change is Gonna Come” finale, where artists and fans — some attending from as far away as Australia and Europe — sang together, facing the future with communal resolve.