Hedvig Mollestad, Jo Berger Myhre and General Post Office shake up Oslo Jazz Festival

Early programmes were heavy on dixieland and bebop. In the festival's offices, the inaugural poster hangs beside a photo of Cab Calloway in white tie, grinning a Cheshire Cat grin, following an appearance in 1987. Nowadays the programme is considerably more open. Straightahead stars still feature – the festival's charter demands it – and this year's bill included Kenny Barron and Fred Hersch. But Sons of Kemet were also in town, along with numerous bands from Norway's trollish experimental scene.

On the final weekend, most of the gigs took place in Sentralen, an old bank recently transformed into a centre for arts and culture. It's an amazing venue – a mix of edgy and grand – all marble staircases and chandeliers, steel gantries and exposed brick. Portraits of purse-lipped bank managers hang in the bar. One of the performance spaces is the old vault – still guarded by the original metal blast doors, with bolts as thick as your arm. On Friday night guitarist Hedvig Mollestad (pictured top) made them shake. Standing alone in the middle of a dendritic sprawl of effects pedals she explored brutishness and beauty. Angular riffs, degraded by tremolo, crashed against the walls like chunks of masonry, tender jazz ballads drifted amongst doppler-warped growls and finger-picked blues lines brought echoes of rust belt Americana. The heaviest moments were like two punk bands soundchecking at once.

Solo sets were a theme of this year's programme. Armed with double-bass and looper, Arild Andersen opened his with an impressionist take on Ornette Coleman's 'Lonely Woman' – all brittle pizzicato and sonorous bowed fragments that bled ink into the room. A late-night duo set from bassist Jo Berger Myhre and Icelandic drummer and electroncist Ólafur Björn Ólafsson (above) was equally atmospheric. Ólafsson played thumping grooves, drones and jangly electronic loops as Berger Myhre added plaintive quarter-tone sweeps and ground his bow into the strings – producing sounds like the creaking, sub-bass groan of an icebreaker.

Danish guitarist Jakob Bro explored a tranquil soundworld over at the Nasjonal Jazzscene Victoria, a charming old cinema home to one of the city's main jazz clubs, but now tragically hidden behind the rashy bulk of a supersized TGI Friday's. There was a lovely looseness to the music, drawn from Bro's latest album, Returnings. It felt like everyone was wandering off on their own, expanding the soundscape in different directions. Palle Mikkelborg added vapor trails of trumpet and flugelhorn. Bro played woozy, Scandi-blues guitar lines and Jon Christensen gently flailed at his cymbals. Thomas Morgan's abstract bass solos were a highlight. I love the subtle tension he creates by hesitating over notes and the delicate way he plucks the strings.

The most open performance of all was a rolling, four-hour jam session run by local improv night Jazz In Khartoum. A theatrical duo called Agbalagba Daada (a Nigerian phrase that translates as "old wise men") came on first. Their set was like a wonderfully weird dream – nothing made sense, but you accepted it all the same and soaked up the sounds: the vocal shouts and the overblown trumpet lines that had the duo in fits of giggles, the rattles, the clacking stones segued with kisses and mouth pops, the primal drum beats, gusts of wooden flute and buzzing jaw harp grooves. It was richly expressive and above all fun, without a whiff of the self-serious pretension that sometimes accompanies free improvisation. There was a particularly brilliant moment when they tried to win back a crying child in the audience with a birdcall whistle.

I made several more discoveries in the Sentralen's atrium bar, where free Nordic Showcases were running throughout the weekend. There were a few visitors, including prodigious Scottish pianist Fergus McCreadie and his trio – who segued virtuosic modal burners into expressive ballads and plundered Scotland's folk tradition for silvery reels. And then there was the dubiously-named General Post Office (above) – a young quartet formed at Bergen's Grieg Academy, whose mix of savage free improvisation and rough-as-guts blues sounded like Peter Brötzmann, Cecil Taylor and Howlin' Wolf. Sax player Aksel Øvreås Røed shredded notes and maniac pianist Isach Skeidsvoll all but demolished his upright piano. With the boards removed, you could see the hammers flailing. It was a brilliant mix of in and out – wild and abrasive, yet steeped in blues tradition. I'm not sure what the reactionary authors of Oslo Jazz Festival's charter would have made it, but I was grinning a Cheshire Cat grin of my own.

– Thomas Rees