I have seen that some people are asking questions about assembly programming using the Z80 CPU. I used it years ago. It it still being used in new pieces of hardware or is it totally obsolete?
Yes, the TI-84+/TI-83+ line of graphing calculators (besides the CE, which uses the faster eZ80 processor) use it: https://en.wikipedia.org/wiki/TI-84_Plus_series
Zilog still appears to sell the Z-80 though it does look like they're mostly selling the eZ80 in that line which is compatible but much improved.
Hobbyists still use it and there is even a kickstarter for building a ZX Spectrum clone: https://www.kickstarter.com/projects/1835143999/zx-spectrum-next However, they don't technically use the Z-80 but a 100% programming compatible clone using an FPGA. Certainly that's still a Z-80 as far as the programmer is concerned.