Actually, much of the high level implementation (e.g. Above GDI) is shared between the Wine and Reactos projects. There are programmers on both projects that make sure changes are sync as Reactos is providing Wine with greatly enhanced low level compatiblity and Wine is providing a complete GUI layer for Reactos to run apps and their explorer shell.

The most interesting part of Reactos is the binary interface duplication all the way into the kernel level. Where wine calls linux/un*x system calls, essentially emulating a function, Reactos has built the exact same substrate within which all their code lies. Due to the API restrictions, much of the functional guts of the functions (esp, API functions) tend to match closely to Microsoft's code (per the DDK samples). The main differences has to do with side effects that Reactos must find to duplicate, which should not be relied on in the first place.

WCFF