Oslo has one of the most active software development communities in the world. For software developers that care about their profession, there are plenty of interesting things happening every week. Here are some activities, groups, meetings and conferences worth mentioning:
The Oslo XP Meetup and The Oslo Lean Meetup often invites hot-shots to present stuff about agile and lean software developement, but we also have small gatherings and programming experiments. By far, the biggest and most active community is javaBin, they have an active website and monthly meetings. The javaBin people are also responsible for organizing the big annual JavaZone conference which attracts more than 2000 delegates. Den Norske Dataforening is the old norwegian computer association, they have a few interesting meetings and they also organizes the annual Software conference. On smidig.no you find an agile software developer community, many of these people are also involved in organizing the Smidig conference. The Ruby community is also strong, and recently there was a Ruby Fools conference in Oslo. We even have a C++ Users Group. The Norwegian Developers Conference will probably sell out at around 1k delegates in June. I should perhaps also mention UXnet Meetup, Norwegian .NET User Group and Norwegian UNIX User Group. Last, but not least, a lot of us meet at Bilabong (Bogstadvn 53) on Tuesday evenings every odd numbered weeks to drink beer.
I am an active member of around half of these groups. Knowing norwegian is not a requirement, since many of these events are in english. If you find yourself in Oslo one day - feel free to contact me and I will introduce to the geek-life of Oslo.