1. State-of-the-art garbage collectors, which enable good implementations of lock-free data structures.
2. Excellent implementations of lock-free data structures (like ConcurrentLinkedQueue and ConcurrentSkipListMap) and other concurrent data structures (like ConcurrentHashMap).
3. A state-of-the-art work-stealing scheduler (ForkJoinPool), excellent for both parallelism (as used by Java 8's streams) and concurrency.
4. A cross-platform memory model specifying memory visibility across threads.
5. Access to CPU concurrency primitives like CAS and memory fences.
These building blocks are a great foundation for any concurrent application.