Apart from surplus/new Z80-clones that are quite easy to find, many emulations depend on software implementations of the Z80:
* [https://zxe.io/software/Z80/ libZ80] Ultra accurate ANSI C implementation
* The [[T80]] is a [[VHDL|VHDL]] implementation of the Z80 and Z80A, finished in 2002 on [[OpenCores|OpenCores]]
* [[arnold]] uses [[InkZ80]], written in C++ (apart from the author-designed C simulation)