I read a bit about the history of Monero and how it forked away from bytecoin/bitmonero in 2014. I also remember that there was another currency using the cryptonote protocol called "Boolberry" at that time. Right now cryptonote appears to be a Monero exclusive, though I know that's most likely not correct.
So what's the status of other dead/alive cryptonote implementations? Are there other actively developed currencies based on it? If so what's their name, purpose, main differences... ?
There are many other CryptoNote coins but their communities, usage, trading volumes and hashrate are much smaller than Monero. Here is a chronicalogical graphic of many of the coins and from where they were forked: https://en.wikipedia.org/wiki/CryptoNote#/media/File:Forks-tree-fixed.png
You mentioned Boolberry, which like Aeon was an innovator in the area of pruning. Boolberry was popular early because (in addition to pruning) it was the first CryptoNote coin with a working (but very basic) GUI. Its developer has been inactive for some time. Aeon has a visible lead developer (smooth) that is also a Monero core developer, so Aeon has received far more attention than Boolberry recently.
Many CryptoNote coins appear to have been created by the same parties: https://bitcointalk.org/index.php?topic=740112.0
Measured by Bitcointalk activity, I would estimate the most active CryptoNote communities are currently:
All have operational blockchains and varying level of developer activity or complete absence of activity.
