I recently picked up Understanding AJAX by Josh Eichorn. Josh is a core ClearHealth developer with Uversa. I am about halfway through it and it is an excellent reference for any web-based EHR developer. AJAX holds the promise of making a web-based EHR just as interactive as a thick-client application. Understanding AJAX covers the basics of AJAX and then spends a lot of time discussing the various AJAX libraries available and how to make use of them. Because so many languages and libraries are covered, there is almost no FOSS EHR project that could not benefit from the techniques described.
This is quite an accomplishment for both Josh and Uversa.