What a great concept! In a walkway under Nørrebrogade (at the start by Dronning Louises Bro) there is a Free Shop (Gratis Butik).
The concept is quite simple – if you see something you like and need, you take it, if you have something you don’t need or want you can place it in the shop.
When I was there earlier this week there was assorted clothing and a few books.
And for the non-danish speakers Ta & Gi is short for tag og giv, meaning take and give.