cc0. cc0 is a compiler targeting Layer Zero which is a general-purpose substrate for cloud computing. cc0 compiles c0 code to i0 code. c0 is a variation of the C programming language with some extentions to support language-level multi-tasking and other mechanisms in Layer Zero. i0 is a ISA for Layer Zero which unifies myriads of nodes in the datacenters to form a big virtual machine.