Openkore.com

dll injected:
OpenDefender
Ragnarok Online Plugin System (ROPS)

other:
kRO without the "IE activex plugin crap" php script

Replay Tool [by DeniZka](tool to replay packets from server smartly):
pRO_XY

P.S.:
Note: Update the link to official Page on rofan.ru

Tsukuru is a Lua based advanced macro tool for Ragnarok Online that you can interfere any incoming and outgoing packets, edit them or even block them via internal scripting. Check wiki page to find more information.

tkool by renjfk (Soner Köksal)

also:
anti bot cracking by kr105 (Carlos Pizarro León)

The Tsukuru -- RenOS (tkool) is using own ws2_32.dll implementation and a proxy tool.
This is no good in situations of Custom Protections that are wide used.

But that Brazilian Blog is more interesting =)

The tktool reminded me of the stuff i used to do with xkore 2. (but the tktool method is probably more lightweight)
Its also reminded me of ROPS but with an actual scripting language (lua)
Oh, looks like latest ROPS source code was actually released

I probably should have posted these posts here
EDIT: nvm, merged the topics

I coded ROPS and meant to always keep the latest source posted. It was provided as-is for people to change/learn from however they wanted. It is pretty messy/bad in a lot of ways. It was only actively developed for a few days, and then I'd work on it for a day or two and put out a new version with long delays. It was adapted from a stand-alone program I had made that injected in to the client. It was designed as an ARETool replacement when iRO added encrypted prefixes, and ARETool modules worked in it initially (not sure if they do now). I made it for a few friends, but they all stopped playing so I haven't touched it. I haven't really played RO since 2007ish.

It was also the first thing I ever coded in C/C++ (lol). I leaned too hard on existing resources a lot of the time. Wished I gained more reverse engineering experience. The initial client thing I did do mostly on my own. I didn't even look at kore source. But ROPS bases a lot of the code on external things.

iRO has ROPS included in its client now, and it has a version of the nospam module as well. The ROPS in the iRO client is rewritten but based strongly on the ROPS code.