MLDonkey

MLDonkey introduced a method to connect to several servers simultaneously, thereby increasing search efficiency greatly. This was at a time when servers were quite small, and already strained (mainly by bots). Too many users, a few servers, new solutions needed.

Later on, certain pretentious server admins became more and more interested in the numbers of users assigned to their servers, rather than in the efficiency of the network. This meant that a client connecting to more than one server was a threat to their internal "high score" competition of served users.

Complaints started to come in from eDonkey users about MLDonkey being too efficient, i.e. utilizing an unfair amount of network resources.

This probably has to do with the extreme reluctance of the developers of eDonkey2000 to improve their product, which led to larger and larger servers, instead of following the approach MLDonkey stood for: increasing the connectivity of the network as a whole.

MLDonkey also features a way to exchange file sources between clients, thereby making the servers less important.