Singularity is an experimental operating system developed by Microsoft Research between July 9, 2003,[3] and February 7, 2015.

[4] It was designed as a high dependability OS in which the kernel, device drivers, and application software were all written in managed code.

The lowest-level x86 interrupt dispatch code is written in assembly language and C. Once this code has done its job, it invokes the kernel, which runtime system and garbage collector are written in Sing# (an extended version of Spec#, itself an extension of C#) and runs in unprotected mode.

[5]: 4,11,35 Protection in this system is provided by a set of rules called invariants that are verified by static program analysis.

Most of the invariants rely on the use of safer memory-managed languages, such as Sing#, which have a garbage collector, allow no arbitrary pointers, and allow code to be verified to meet a given computer security policy.