Thought this was the perfect place to share a project I've been working on for a few years: https://asm-editor.specy.app
It's an interactive online IDE for many assembly languages, currently M68K, MIPS, RISC-V and X86 (I need to improve X86). It has a ton of features that are made to teach assembly programming, and it can be embedded in other websites.
No Z80 or 6502?
Not yet* https://github.com/Specy/asm-editor/issues/25 And 6502 is a bit harder
With such a domain name, it should have been Z80 :)