HotKeys is a javascript input capture library with some very special features, it is easy to pick up and use, has a reasonable footprint (~3kb), and has no dependencies.
jSignature is a jQuery plugin that simplifies creation of a signature capture field in a browser window, allowing a user to draw a signature using mouse, pen, or finger on touch enabled devices (e.g. iPhones, iPads or Android devices).
jSignature captures signature as vector outlines of the strokes. Although jSignature can export great bitmap (PNG) too, extraction of highly scalable stroke movemmovement coordinates (aka vector image) of the signature allows much greater flexibility of signature rendering