Assembly language

Assembly language is not a proper "programming language" per se, but rather a tool that allows you to write machine code using short, semi-human readable memenomic instructions and link the into an executable, as an alternative to having to write streams of ones and zeroes and load them into memory. This effectively means that not only do each microprocessor family have their own assembly language format and instructions but also each processor version inside that family has its own instruction variations, but in addition to that different assemblers may use different mnemonic substitutes for each processor instruction.

OS/2 Hosted Assemblers
Commercial
 * IBM Assembly Language Processor (ALP)
 * IBM Macro Assembler/2
 * Lattice LASM
 * Microsoft Macro Assembler (MASM)
 * TopSpeed TechKit
 * Turbo Assembler

Open Source
 * GNU Assembler
 * NASM Assembler - LGPL
 * Wasm, JWasm

OS/2 Hosted Cross Assemblers
Open source
 * 8085 Cross Assembler
 * CC65 - Contains a 6502 cross assembler

OS/2 disassemblers
Freeware Open Source Shareware
 * DISA - i86
 * AVR Disassembler - AVR
 * BeaEngine - i86/AMD64
 * PIC Disassembler - PIC
 * IDA - i86/AMD64

OS/2 development systems with built in assemblers

 * Cabot UCSD Pascal - Commercial
 * Open Watcom - Open Source
 * Pecan UCSD Pascal - Commercial

Aids

 * FWKTL - Allows OS/2 to run COM like self modifying code

Libraries, bindings and stubs

 * LZ4 - Compression library

Editor support

 * Boxer - x86 and AT&T DSP32SL (Included by default) - Microchip 16C715, Mitsubishi 37451, PL/M-51 and 8051 (Contributed, requires download)
 * Enhanced Editor - Has automatic "tagging", generates automatic code summaries with links and other ASM goodies.
 * FTE - Has support for syntax highlighting, code folding and syntax-aware auto-indent.
 * jEdit - Java based editor - m68k, Macro32, MCS51, R2000, Parrot and x86 built in, 6502, AVR and PIC optional.
 * Lugaru Epsilon - i86 syntax highlighting, code folding and syntax-aware auto-indent, 68HC12 available as a separate download.

Assembly language related programmer's utilities

 * Exuberant ctags - Creates index files out of assembly language source files - Open source

DOS hosted assemblers

 * Pharlap 386|ASM/LINK
 * A86 - Commercial/Shareware
 * Assembler ASM
 * Arrowsoft Assembler - Public Domain
 * CHASM (Cheap Assembler)
 * Intel ASM386
 * IBM Macro Assembler
 * Microsoft Assembler
 * Wasm, JWasm
 * Phoenix Pasm86
 * TopSpeed TechKit
 * Borland Turbo Assembler

DOS disassemblers

 * ASMGEN (Gersbach, Damke) - Public Domain
 * DASM (Williams)
 * DIS86 (van Zandt)
 * MD86
 * PICDIS-LITE - PIC - Shareware
 * Yilmaz Disassembler

DOS development systems with built in assemblers

 * ASMEDIT - Freeware
 * Open Watcom - Open Source
 * Pecan UCSD Pascal

Libraries, bindings and stubs

 * LZ4 - Compression library

Editor support

 * Boxer - x86 and AT&T DSP32SL (Included by default) - Microchip 16C715, Mitsubishi 37451, PL/M-51 and 8051 (Contributed, requires download)
 * FTE - Has support for syntax highlighting, code folding and syntax-aware auto-indent.

Publications

 * Murray; Pappas: Assembly Language Programming under OS/2 – McGraw-Hill 1988, ISBN 0-07-881412-X
 * Leventhal: Assembly Language Programming under OS/2 – Bantam 1989, ISBN 0-553-34578-8
 * Holzner: OS/2 Assembly Language – Brady 1990, ISBN 0-13-642505-4

Links

 * Working in Protected Mode - A tutorial for DOS programmers, but helpful for OS/2 newbies to a degree.
 * Sandpile.org - Lots of info on i86 and AMD64 instructions.
 * The Art of Assembly Language Programming - An often referenced 80x86 Asm on-line tutorial and reference, note though that the examples are in a HLA format, a specific type of assembly not available for an OS/2 toolset.
 * USENET: [news:comp.lang.asm.x86 comp.lang.asm.x86]

Standards
Unlike most other languages the assembly language is not an artificial language that requires standardisation but rather an implementation of a practical reality that came into existence when a specific CPU was designed and manufactured, so the standard is the actual documentation of a hardware implementation. That means for 8, 16 and 32 bit processors the "standard" are the processor and programming manuals from Intel while for 64 bit assembly language you need to look towards similar manuals from AMD.