This is the Custom Heater Block by Mr Anders Olsson, discussed at large in this tread in the Ultimaker forum.
Installing it lets you change nozzles sizes on the Ultimaker 2 or Extended in less than 20 seconds.
“The Olsson Block” ships with one “JET 040″ standard nozzle seen in the picture. This nozzle works with your existing configuration right away. Also included are the tools you need. You must also have the UM2 standard tool which came with the printer; the tiny Umbraco style “key”. You can order a UM2 or Ext. and get a free Olsson Block starting from November 4th!
“The Olsson Block” is a new hotend for your Ultimaker2. This upgrade makes it possible to very quickly and easily change nozzles on your printer. This makes it possible to achieve much more detailed prints or considerably faster extrusion rates depending on the nozzle you choose. The upgrade can be especially suitable if you want to experiment with materials that cause more wear than normal on the nozzle, such as XT-CF20.
The standard kit comes with a 0.4mm nozzle which matches the size that the UM2 and Ext. ships with. In addition it includes nozzles in the following sizes: 0.25mm, 0.60mm and 0.80mm. These can also be bought separately.
The standards kit comes complete with all the pieces you need except for an allen key which was supplied with your Ultimaker2.
Much more information can be found in the following thread that was started by the creator Anders Olsson:
This video shows you how to install it: