Here in the very first posting of this thread you will find attached the latest version of the ZX-IDE as attachement. This will be updated as necessary. And I will keep an index of the content here for a better on case reading for important sections and you don't have to read all from A to Z.
Index of content:
Beginners assembly section
=> Edit and compile (assemble)
=> Audio transfer to ZX81 or ZX80
=> Listing
=> Addressing Spaces I
=> Data definitions I
=> Data definitions II (blocks & more)
=> Variables and Constants
=> Labels
=> Use of Media Player for transfer
=> ZX Emulator EightyOne
=> ZX emulator EightyOne - hints for using
=> Z80 Assembler - undocumented opcodes
ZX81 BASIC programming
=> ZX81 BASIC, REM, _asm
=> ZX81 BASIC, line numbers, labels
=> ZX81 BASIC, RAND, USR
=> ZX81 BASIC, format, AUTORUN, _noedit
=> ZX81 BASIC, _hide
=> ZX81 - different context of ZX BASIC and assembly
=> ZX81 PRINT, number formats , calculations
=> ZX81 mathematics and functions
=> ZX81 startup variables
=> ZX81 BASIC, variables, LET statement
=> ZX81 BASIC, labels as line numbers (GOTO, etc.)
=> ZX81 BASIC, graphic chars, special chars, charset
=> ZX81 BASIC, IF-THEN statement, comparison, STOP
=> ZX81 BASIC, FOR-NEXT loop, STEP, FAST, SLOW
=> ZX81 BASIC, VAR definition in memory I
=> ZX81 BASIC, VAR definition in memory II
=> ZX81 p-file converter
ZX80 BASIC programming
=> ZX80 BASIC, line numbers, REM, _asm
=> ZX80 BASIC, RAND, RANDOMISE, USR, labels
=> ZX80 BASIC, AUTORUN, _noedit, _hide
=> ZX80 BASIC, overview and instruction set implementation
Tips & tricks for experts
=> Batch file execution after compilation, ZXpand token
=> Useful macros for PUSH and POP
=> Macro for data manipulation and string formatting
=> Useful macros for jumps and loops
Here the original posting:
I announced to write a tutorial as I did on the german board and here it is.
First you should get the latest version here which is always in this first posting of the tutorial thread.
Second the name changed from ZX81-IDE to simply ZX-IDE or FASMW-ZX.EXE as it will support not only programming of ZX81 but also use of ZX80 (already prepared) and hopefully the ZX Spectrum later this year (as I am a new owner of a working ZX Spectrum 48k).
The installation is very simple, just unpack the ZIP archive and get started with FASMW-ZX.EXE which is a nice IDE with integrated text editor and multiple source file support (can be opened up to 10 or more sourcefiles to work on). The external program LISTZ80.EXE is started with a keypress (F8), generates a nice listing and open it automatically in a new IDE window. The FASTLOAD.BIN file is needed for the Fast Loader option in the IDE which speeds the audio transfer by factor 25 from about 40 byte/s to up to 1kByte/s. There are 2 demo files in the ZIP archive, the ZX81DEMO.ASM as a simple program to load into the ZX81 and the ZX81ROM code as source which can be compiled to the 8k binary with the IDE. Maybe if someone wants to improve his Zeddy.

The subdirectory SINCL-ZX contains include files for use with ZX81 programs which contain defines, variables and memory sections like the D_FILE.
Main purpose of adapting the original FASM IDE x86 version to Z80 and ZX BASIC was the use of a powerful development engine to enter and modify source code, simplify development process without difficult configuration of several command line programs, linkers, batch files and so on. There is now also the use of the emulator integrated which can be started with the actual processed source simply with a keypress (F8).
The flatassembler as base is a powerful assembling engine mainly used for modern x86 processors and meanwhile as ARM version available too. I did the porting to Z80 and ZX BASIC (ZX81 first). The assembling process is divided into 4 internal steps and consists of a preprocessor with processing of macros, a parser to convert source statements into assembler structures, multi-pass assembler to resolve the code and formatter to put the code into several output formats. Here is only flat binary useful but has also some linker formats (for example ELF). The Z80 assembler supports the official Z80 mnemonics or instructions released by ZILOG in the late 70ies / early 80ies and in the meantime the undocumented opcodes as well.
This thread will replace the (non-existing) manual.

Official documentation of flatassembler:
http://flatassembler.net/docs.php?article=manual
Discussion board of flatassembler for special questions:
http://board.flatassembler.net/index.php
Version in attachement:
ZX-IDE 1.71.01u.Z80 (08/2017)