Pintask

With Pintask you can write your own extensions using Javascript + Meteor API. MongoDB access in browser included. You can save time with quick actions for cards and lists.You get an advanced Kanban board for free. Plus, you get free nesting of lists and cards as a bonus.
You may install paid extensions, for example: Mirroring of lists and cards or Hands-free time tracking. Extensions are installed on per-user basis, so your teammates will need to install extensions for themselves. It’s like App Store, where each person installs his own apps.
Paid extensions have a free trial period (duration varies from extension to extension). After trial expires, you need to buy monthly subscription. There are also free extensions, which obviously cost nothing. Plus, you can write your own extensions.