Where can I find resources for building game editors?

Pretty self-explanatory title … the exception being that I am on Mac. From the looks of it nearly everything here is windows. I have read a few of PureIso's threads and found them quite informative. At least what I could glean from them. I'd really like to find some resources that are cross-platform, so that I might develop some cross platform editors, if at all possible. I am looking for something for n00bs, preferably, I have some experience but the more explicit the instructions the better.

Also I am using Velocity as my save editor, so any info related to it would be absolute best. However, anything is better than nothing, so hit me with your best shot. Lastly, I am interested in opinion regarding hex editors for Mac. Currently I am using Hex Edit, a brass tacks, freeware. It works. I have also been dabbling with Synalyze it, which is far more comprehensive but is paid for and on a timed trial.