Freehand Drawing Library
The FDL makes it easy to integrate smooth, freehand strokes from mouse, touch, or device inputs into an application. It supports fixed- and variable-width strokes as well as various line decorations such as dashes and dots. The easiest way to become familiar with the library and its capability is to read all about it. Here are some links to my old blog that highlight the development.
Although I generally only license the FDL to clients, I am open to occasionally adding developers to the private beta. There is a modest three-figure license fee involved. Once you are in the beta program, then upgrades are free for life. If you are serious about joining the program, then you may contact me at theAlgorithmist [at] gmail [dot] com for more information.