MS Paint is a free painting tool which comes in build in Windows. If you are looking for an alternative portable freeware paint tool, you can try out HyperPaintNet. HyperPaintNet is a simple freeware tool which is quite similar to MS Paint and also has a nice feature of using it as a multi-user, which in turn means you can connect to internet, share the IP of the server and other users can connect to this server and edit the drawing.
Once you connect to the server and give other users your IP, you can tell them to connect to it so you can all share the same drawing area. Every modification on one client will be updated instantly to all other clients (and to the server too) automatically.
There is also some nice effects too, like: swap colors, invert colors, brightness, darkness, black and white, colorize, solarize, gray scale, rotation, etc.
