I am just getting started playing with rAthena, so far it's been fantastic.  Plenty of docs on the server components, and I was able to get the majority of that running in a matter of minutes.   However, there is a significant lack of documentation for creating clients that doesn't involve reading lots of linked posts and a bit of prayer.   I finally managed to get the latest kRO (20160124) working with a custom client (2015-10-29), modified using NEMO, and was able to connect to my server a