Xaja is an open source PHP library that implements reverse Ajax functionality. It uses long-lived processes and a message broker to push data from the server to the browser without page refreshes. Xaja provides custom tags and attributes that simplify reverse Ajax development and allow controlling the browser DOM from PHP code. While resource intensive due to its use of long-lived processes, initial tests show it can handle around 10 concurrent users. The developers plan to expand its feature set and improve performance.