First, a little background 
Basically, currently I am working on an action, puzzle game. It is both 3d and has 2d scenes. Pretty much a JRPG but with action combat. To draw the 2D characters, I draw a sketch on paper, scan it and draw the lineart on PC. Since I do not have a tablet, drawing lineart in GIMP or Inkscape, with mouse is a bothersome work. A good program for lineart is eg. PaintToolSAI, which is, however, not free.
Thus… you guessed it - let’s just make one 
: ZManga is an app for drawing lineart with mouse. But reinventing the wheel did not end with just that - since I really like Blender’s user interface I ended up making Swing UI look like Blender’s. 
So there you have it.
Thus I am posting it here for you who are making a game with anime/cartoon characters, you might find this tool helpful.
Finally you can check it out(along with a screenshot - btw I am still learning how to draw) at: