Visitstockholm – the Official Visitors’ Guide to Stockholm 
https://www.visitstockholm.com/en/See–do/Events/

Vamos – The event app – Stockholm
http://www.getvamos.com/stockholm

Eventbrite
https://www.eventbrite.com/d/sweden–stockholm/events/

Meetup
http://www.meetup.com/cities/se/stockholm/

Eventful
http://eventful.com/stockholm/events

Gratis i Stockholm
http://www.gratisistockholm.nu/http://www.gratisistockholm.nu/

Time Out – Stockholm
http://www.timeout.com/stockholm/features/338/festivals-events-in-stockholm

I Love Stockholm
http://www.ilovestockholm.se/gratis_i_stockholm.asp

Whatup
http://whatsupsthlm.se/

Totally Stockholm
http://totallystockholm.se/

Stockholm Stad
http://www.stockholm.se/-/Kalendarium/