The gist of the idea is to run the whole user environment, desktop and all, inside WINE. So it's something like a bare-metal WINE sitting on top of the Linux kernel, with just enough plumbing to connect them up. This is significantly different from the current way, which is to run a completely Linux-based stack - the kernel, an init, a userland, a Linux display system, and a Linux desktop, and then run Windows programs inside that.
Pear Linux was a French distro by David Tavares, based on Ubuntu and GNOME but heavily themed with custom fonts, icons, menu layouts, and more, all intended to make it visually resemble Apple's Mac OS X as closely as possible. As DistroWatch records, it went through some seven releases between 2011 and 2013, before Tavares announced that an unnamed company had bought it, and the distro vanished. Some contemporary reviews of PearOS 3.0 (2012), PearOS 7.0, and PearOS 8.0 (both 2013) - especially their screenshots - will give you an idea of how well it accomplished that. The idea has enduring appeal. After it disappeared, there were attempts to revive it, including Pearl Linux and Clementine OS, both in 2014, but neither got far.