The RTSJ (Real-Time Specification for Java) provides features for real-time Java programming like real-time threads with precise scheduling, memory management schemes like immortal and scoped memory, asynchronous event handling, nanosecond timers, and direct access to physical memory. It addresses issues in the standard Java SE like unpredictable garbage collection and enables hard real-time capabilities with latencies of 20 microseconds and jitters of 10 microseconds. The RTSJ is used in applications like real-time CORBA, Mars rovers, and medical devices.