http://tslib.berlios.de/
Tslib is an abstraction layer for touchscreen panel events, as well as a filter stack for the manipulation of those events. It was created by Russell King, of arm.linux.org.uk. Examples of implemented filters include jitter smoothing and the calibration transform.
Tslib is generally used on embedded devices to provide a common user space interface to touchscreen functionality. It is supported by Kdrive (aka TinyX) and OPIE as well as being used on a number of commercial Linux devices including the Nokia 770.