An implementation of the popular Earliest Deadline First (EDF) scheduling algorithm or the Linux kernel. It is still experimental code, and it is still continuously being improved, but it already is a fully-working solution for supporting typical real-time applications in GNU/Linux environments.
Actually, SCHED_EDF was the initial name, and it has been changed to SCHED_DEADLINE upon request of the kernel community itself (see https://lkml.org/lkml/2009/9/22/214).
People confused with I/O Scheduler (IOSCHED_DEADLINE)
:)