How is Adblock Plus related to Adblock?
The development of Adblock pretty much stopped in 2004. When more and more people demanded improvements Michael McDonald came up with Adblock Plus 0.5 — basically a version of Adblock with whitelisting, filter subscriptions and several other useful features.
This version of Adblock Plus was still based on Adblock, which set hard limits to improvements. Quality of Adblock being... shall we say... less than adequate a complete rewrite was desperately needed. That came with Adblock Plus 0.6 — a completely new extension with focus on being easy to use, stable and secure. For various reasons many enhancements from Adblock Plus 0.5 didn't make it into the original release of Adblock Plus 0.6 but this changed with Adblock Plus 0.6.1.
Michael McDonald, the developer of Adblock Plus 0.5, has changed to the Adblock project and is trying to develop it further now. For that reason starting with Adblock Plus 0.6 the main developer of Adblock Plus is me (Wladimir Palant).