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Here you can find a list of links to cases for the Fairphone 2. Discussions on cases can be found here and here.
Legend:
Produced for the Fairphone 2, fits exactly
Does not fit perfectly, but is great in other ways (please specify)
Socks
Pouches / Sleeves
Blum Manufaktur (de) Jeans sleeve by blum manufaktur to be bought on Amazon (de) (delivery to EU only as it seems) , as the shop on the manufacturers homepage still seems to offer nothing (all is out of stock). Available via the local amazon homepages as well: UK, FR, ES, IT
Available in other designs as well, that can be seen on Amazon (de).
User experience: The sleeve fits perfectly, looks and feels fine crafted, microfibre (like used for cleaning glasses) inside. The FP2 can be put in and out without effort, you can grab it easily when foulding the rim a bit, it doesn’t fall out - my model has a rubber belt around whicht makes sure it can’t fall out. I’m not quite sure how stable the rubber belt will be in long time use, but apart from this little uncertainty, the sleeve is perfect for my FP2, manufactured in Germany/local for me means low transportation effort and costs, environmentally and wage fair sleeve for the fair phone 
price 20 Euro is not cheap but in my opinion ok for the quality and circumstances.
Feuerwear (Deutsch & English) (dealers worldwide). The Mitch 10 is the official fit for the Fairphone 2. Some other people recorded success with the Mitch 6 while others found it too tight. YMMV.
Mapbagrag (de) (delivery to EU, CH, NOR, USA, CAN) Two different paper sleeves and pouches tailored for the FP2 (“bagflip”, and " flip") that come in various designs. The sleeves are made with the help of Austrian social enterprise Jugend am Werk by special(-needs) people. They offer custom-made stuff as well. Note: Some customisation options appear to be missing from the English shop interface. (I could not check, if this still is true.)
[Edited because Mapbagrag by now offers flips specified for the FP2; added direct link to the shop; should there be a special english-shop site, please add it]
Remark: I bought a flip pocket custom made 5-6" and specified the dimension in the commentary. I like it and the phone fits perfect.
FitBag (de) (wordlwide delivery) All pouches are hand-made and fit to the dimensions of the phone that you specify at purchase. You should just keep in mind, that for the FP2, dimensions are 143 x 73 x 11 mm³ (HxWxT), however, with the rubber band of the case, 12 mm thickness are more appropriate.
Different materials (from leather to fake fur) and colours are available (all in all more than 70 different styles).
Flip / Folio / Wallet Cases
Mapbagrag (de) (delivery to EU, CH, NOR, USA, CAN) See above. Mapbagrag offers a flip case as well.
Mobilemagic (ch) (delivery to EU) Swiss shop offering flip casesmade of leather, canvas and textile.
Offers covers for FP1 and FP2 and other accessories like protective foil and chargers (Hoco; would be interesting to know, if those chargers work).
[Edited to standardize the entries and added Mabpagrag to FlipCases]
Pela make a compostable case for the iPhone (“made of Flaxstic®, which is comprised of GDH-B1 compostable bioplastic elastomer and flax straw materials”); could they be persuaded to make one for the Fairphone?