I had a Brazilian server some years ago with the same concept: mix missing Final Fantasy classes on Ragnarok. The server worked well and I was able to create 2-3 and 2-4 classes fully playable. The problem I faced was the the outdated client (I was using X-ray) and a weird freezing bug that I could never fix. So I put project on hold until I could find a way to bring it back.
With roBrowser I saw an opportunity for this. After some tests I can see the client is still lacking a lot of functionalities and updates, so I will probably get back to the same problem again in little time. But I will do it anyway (I am bored).
The main reason for this project is to bring new classes to the game. A mistake I made in the past was starting by the 2-3 and 2-4 classes (that forced me to soon include the transcendent for them). This time I will start by the expanded classes. To make my life easier I will not include the 3rd classes (Pre-Re).
Here's the version 2.0 custom classes list (the RO's original remain):
Red Mage / Red Wizard: A mix of Mage and Acoyte with fencing melee skills.
Dark Knight / Dark Lord: A reverse crusader. Sacrifice his HP to cause damage.
Necromancer / Lich: They can summon and become the undead.
Shaman / Spirit Master: Nature HP and SP healers.
Mediator / Diplomat: They use the voice as the main weapon. Can use bows and guns.
Scout / Pathfinder: Long-ranged support class. They can create tents, bonfire, craft bows and enhanced maps.
Geomancer / Geognostic: Use the terrain as their main weapon for heavy magical damage. Can also find and enchant precious stones.
Juggler / Jester: They can toss any piece of equipment on the enemies. Each type of equipment inflict a different status ailment. They can also counter long-ranged attacks.
Sky Pirate / Corsair: They can create personal airships for the party. Create canons to help on battlefield and debuff enemies. Able to equip daggers, bows and guns.
Blue Mage / Blue Wizard: They learn skills from enemies (and homunculus) for life. Also can reverse HP and SP.
Oracle / Prophet: Debuff masters. Can also equip pole weapons (cause more damage to enemies with more DEF).
Time Mage / Time Wizard: Manipulate the time and space. Advanced speed, flee, AGI, cast time reduction, teleport and portal skills
Valkyrie (Dragoon): Expanding the Jump skill functionalities, they can perform multiple jumps to attack.
Arithmetician: Perform calculations that can result in heavy magic damage (to enemies and allies matching the criteria).
Judge: They can basically change mapflags at will (block usage of any magic, specific skills, items, area magic, etc) with their yellow and red cards.
Onion Knight: don't have any active skills, but a passive skill for each type of class on the game. Each class on the party will give the Onion Knight a bonus. For example, they can get 7 STR bonus for each Swordsman on the party. They can also equip any weapon.
Mime: The Mime target a player on the party and them will be copy every action and skill use of that player with no SP, HP or item needed for the skills. Something like a semi-bot.
Samurai: They draw the spirits from their swords to deal heavy neutral magic damage with debuffs. Can also hold one-handed swords with both hands to deal more damage.
Cartomancer: Turn monster cards on the inventory into active skills. Can also draw cards to decide the fate of the battlefield.
Seamstress: Supportive and crafting class. They can buff fabric equipment and craft clothes.
Chain System: receive more EXP for a same monster defeated multiple times.
Save Crystal / Gate Crystal: basically a Kafra that heals.
Party airships: for the Sky Pirate parties, airships that can be configured with the locations the party want. And can also be customized.
Class swap: A single character can change to and master all the classes. Some jobs requires multiple jobs mastered to unlock.
Limit break: A new gauge that will charge on every hit the character gets. Once full the character can use a special and powerful skill (a different skill for each class branch).
This project is open source just like rAthena and roBrowser. So, anyone who wants to help are welcome.
Github for current client: https://github.com/wjrosa/robrowser-rf2
Website (still with the WP demo contents, but the classes links are real): https://www.ragnafantasy.com/classes/