Server Emulators (Ragnarok Online)

Early Server emulators

ROServer (0006.rar) - Predecessor to 0052.lzh (Server Emulator), presumably the same emulator, but not confirmed.
0052.lzh (Server Emulator) - Predecessor to most of the RO emulators posted on EmuServer Of Ragnarok (EOR) BBS
YARE (Server Emulator) - Based also on a mixture of 0052.lzh and Athena itself.
Athena (Server Emulator) - Originally posted on EmuServer of Ragnarok, Japanese. The progenitor of a very large number of emulators.
I-Athena (Server Emulator) - Athena rewrite/improvement project which was included in YARE and which was based off Athena and YARE code.
Weiss (Server Emulator) - Based on 0052 and Athena.
Apurodani (Server Emulator) - Short-lived emulator which was provided on EOR BBS based on code which predates 0052.lzh. Was largely superceded by 0052.lzh and development ceased very shortly thereafter.
ROSE (Server Emulator) - Relatively obscure emulator which as based off the RO protocol but does not appear to be based off 0052.lzh.

Athena derivatives

AthenaX (Server Emulator) - A Japanese off-shoot of I-Athena (Athena) which was relatively short-lived.
EAthena (Server Emulator) - English translation of Athena which was largely in Japanese.
hAthena (Server Emulator) - Proof of concept emulator based off Athena with various additional features and scripts but never released.
AthenaAdvanced (Server Emulator) - GUI-Based Athena derivative.
OmniAthena (Server Emulator) - GUI/console-based Athena derivative based off eAthena/jAthena, founded by YARE developers.
Project Odin (Server Emulator) - An Athena and YARE offshoot, started by OmniAthena developers
- Project Apollo (Server Emulator) - A revival of Project Odin run by previous developers of Odin and MaSs Zero.
Freya (Server Emulator) - Offshoot of eAthena/Athena focused on stability.
Nezumi (Server Emulator) - Offshoot of eAthena/Athena which was related to trying to provide performance and stability.
SeAr (Server Emulator) - Traditional-Chinese translation of eAthena developed as a separate project.
rAthena (Server Emulator) - Renewal Athena - A successor to eAthena, currently still in development.
Hercules (Server Emulator) - A successor to eAthena, currently still in development.
cHercules (Server Emulator) - A Traditional Chinese version of Hercules.
99MaxEathena (Server Emulator) - A Traditional Chinese successor to eAthena.
Panda Simulator (Server Emulator) - Previously called rAthenaCN, a Chinese successor to rAthena.
Cronus Emulator - The very first Brazilian translation fork of rAthena.
brAthena - The Brazilian translation fork of the Hercules

Weiss derivatives

eWeiss (Server Emulator) - English version of the original Weiss.
DarkWeiss (Server Emulator) - Successor to eWeiss(?)
Fusion (Server Emulator) - Successor to eWeiss(?)
Helios (Server Emulator) - Rewrite of Fusion and Weiss
Vidar (Server Emulator) - Proprietary successor to eWeiss and Weiss
Prometheus (Server Emulator) - Open source successor of Weiss and Vidar

Proof of concept

PQRS (Server Emulator) - An unreleased POC written in C# using multithreading
Rust-RO - A modern emulator written in Rust