Version 2.0 is coming soon!

I have been actively working on version 2 since June 2019. The first public preview will be available in November 2019. The main themes of version 2:

Totally rewitten Visual Studio integration. I removed many annoying issues related to solution loading
Multiple ZX Spectrum projects. You can put more than one ZX Spectrum project into a single solution. While working, you can change the active project anytime.
Boriel's BASIC (ZX BASIC) integration. Besides Z80 assembly, now, you can use ZX BASIC as your programming language to create spectacular games and applications.
New debugging tools. The ZX Spectrum emulator provides two extra options: ULA render point indication, and shadow screen rendering.
New, more modern project item icons

Online Z80 Disassembler. After releasing Assemblex IDE, I noticed it's much easier for users to use online tools. So, I decided to create a browser, online (but also available offline) Z80 Assembly Disassembler! The core engine is just like Assemblex's but if you give it a try with huge programs (I tried disassembling zStart 1.1 and it did it. Simple server-side disassembler for any binary file into Zilog Z80 assembler instructions set. You can upload data and define ORG/START addresses. For Hobeta files input ORG address is autodetected. Output is formatted with SjASMPlus syntaxes and is ready to be compiled out of the box. Z80 Simulator IDE 9.50 is an application for Zilog Z80 8-bit microprocessor that is bundled with an emulator, basic compiler, assembler, disassembler and debugger. Z80 Simulator IDE has extensive program options and consists of a memory editor for 64k memory. So, I decided to create a browser, online (but also available offline) Z80 Assembly Disassembler! The core engine is just like Assemblex's but if you give it a try with huge programs (I tried disassembling zStart 1.1 and it did it in less than a second) you'll notice it's much faster.

Preview 1 will have these limitations:

ZX BASIC source code debugging is not supported yet
Z80 Assembler Output and Z80 Unit Test Explorer is not supported yet
SpectNetIDE is available only on VS 2019 (all editions supported)
Spectrum Scripting Console App project type removed

After releasing Assemblex IDE, I noticed it's much easier for users to use online tools. So, I decided to create a browser, online (but also available offline) Z80 Assembly Disassembler! The core engine is just like Assemblex's but if you give it a try with huge programs (I tried disassembling zStart 1.1 and it did it in less than a second) you'll notice it's much faster. Mainly because Javascript is faster than Python (also depending on the browser, Chrome's Javascript is the faster).

So, where can I find it?
Source

http://www.davidgom.co.cc/z80.html
Right there! Please give it a try, it's online, no downloads! Please give your opinion on it on this topic

Z80 Disassembler Online Training

Z80 Assembler Online

I also have to say it can't open files for now, but that will be included soon (using PHP). If you want to disassemble files use a Hexadecimal Editor like Hex Baker or XVI32 and then copy and paste the code there. Thus, you'll see how fast it is disassembling huge files and applications, perhaps even Operating Systems.