Ceylon has a powerful static type system that prevents bugs while letting developers express: union types, intersection types, higher order functions, mixin inheritance, and enumerated types. The source code for Ceylon and its specification are available from GitHub.
There is a module architecture here for code organization, dependency management, and module isolation at runtime — the language module; i.e., the minimal, cross-platform foundation of the Ceylon SDK, plus a full Eclipse-based integrated development environment.
Ceylon is marked out for its emphasis upon readability and strong bias toward omission or elimination of potentially-harmful constructs. It also claims to have a "unique" treatment of function and tuple types to enable abstractions.
Just prior to this launch King wrote, "Ceylon 1.1 will be all about performance, including language performance, compiler performance, and [David's] ongoing work on IDE build performance. A warning: We expect to break binary compatibility between 1.0 and 1.1. That's not something we do lightly, and it's not something we plan to make a habit of. Changes affecting binary compatibility should occur in major releases, not minor releases. Please forgive us if we break our own rule this one time."