OSNews often reports on small and hobby operating systems. Here is a list for you to vote for the one with the right amount of technical and wider success potential for a bright future. Note 1: The Poll is now closed. Thank you for voting!
Note 2: There are more small OSes around (e.g. µnOS, Athene, Rome etc) but we picked only the non-commercial, “hobbystic” in nature, unique in codebase and architecture and the most well known of the bunch. If you have never heard of these small OSes before, make a search on OSNews about them! Linux and derivatives (e.g. blueeyedos, cosmoe etc) or Plan9 do not fit to the poll because of some of the reasons outlined above.
Update: The AROS choice is now deleted due to a hack by a certain individual in favor of AROS. For your interest, AROS had 5% before it got tampered.