The open source nature of The Mana World allows everyone to use it as a base for creating an own game. A lot of teams have made use of this opportunity.
Active forks
These are projects which are still in active development.
Aethyra
A fork of TMW based on the eAthena branch.
Mundo Dos Dragoes
A portugese fork of TMW based on the eAthena branch.
Inactive forks
These are projects based on TMW which are unfortunately not active anymore.
Sirus Online
A eAthena-based branch formed by people frustrated with the management of Endless Online. It had a quite good start until most players and some developers decided to rather play and develope the original TMW.
Damasca
A project very similar in scope to The Mana World, although programmed in C# instead of C++. When the development slowed down because of insufficient manpower it was attempted to rescue the project by using TMWserv and the TMW client which were already much further in their development. Unfortunately it did not turn out so well.
Evol Online
A french fork of TMW which used the TMW software with a completely new world made from RPGMaker XP graphics. Died due to financial problems.