I have been looking for a free program like this for several months now!!! You have no idea how much trouble you just saved me from trying to get my hand-drawn graph paper maps from the pad to online. You sir, are a scholar and a gentlemen!
I have recently stumbled upon inkarnate myself! The program still needs a bit of work (it would be amazing if there was an "undo" button or if you could change the size of objects), but it is free to use, pretty simple to learn and generally very good!
I have been looking for such a program for ages and am really happy that I found it!
"Give a man a mask and he becomes his true self."
Check out "Scath:Shadow of the Fomori", my current RPG project and the first of my works that will hopefully be published!