This reminds me, a couple of months ago I made my Z80 assembler public on GitHub [1] but never mentioned it anywhere.
It has the usual opcodes and directives, includes, relocation data etc, with a couple of other helpful output files alongside the expected binary one.
Because the driver for it was coding on the ZX Spectrum it will also create tap files with a BASIC loader and loading screen support. And it has a not very featuresome sprite editor built in for the Spectrum screen and attributes. Oh, and a PNG-to-SCR conversion process for loading screens that does a bit of work to show problem areas (as heatmaps).
It's only actually been used by myself and one other person so there may be a few hiccups, but it WOMM :)