Although the NeXT ultimately failed in the marketplace, it introduced several features new to personal computers, including an optical storage disc, a built-in digital signal processor that allowed voice recognition, and object-oriented languages that simplified programming. It's relatively high price of $6,500 limited sales. NeXT Computer Inc. eventually became NeXT Software Inc. and then was bought by Apple in 1997.
@sfleetucker @TheNewsOwl Mach Kernel:
The NeXTSTEP operating system was based on the Mach microkernel, which separated the hardware-level tasks from the higher-level operating system components. Machβs modular design allowed for better memory management and multitasking. By abstracting certain low-level tasks (like memory and process management) into smaller components, NeXTSTEP could run on various hardware architectures, an idea carried into modern OS X/macOS. (don't mention it to @macfate)
@matuzalem @TheNewsOwl I remember it well. And our binaries could be multi platform and the Mach loader would load the right one for the OS. Avie Tevanian was ex-CMU (and my boss for a while). He was a much better programmer than a boss.
@sfleetucker @TheNewsOwl Unfortunately some great programmers can be shit gibbons. 
@matuzalem @TheNewsOwl They were amazing machines. I'm still sad they didn't use the floating menus from NeXTStep in OS X.
NeXT is also why Apple could hop processors at will. They built the base OS to handle different byte boundaries and endianess so it could run on Sparc, Motorola, Intel, RS/6000, and PA-RISC and interoperate without trouble.