Open Watcom Assembler

Open Watcom Assembler or WASM is an x86 assembler produced by Watcom, based on the Watcom Assembler found in Watcom C/C++ compiler and Watcom FORTRAN 77. Further development is being done on the 32- and 64-bit JWASM project, which more closely matches the syntax of Microsoft's assembler.

There are experimental assemblers for PowerPC, Alpha AXP, and MIPS.

Assembler

 * Native support for output formats Intel OMF output formats
 * Supports Intel x86 (Pentium MMX, Pentium III-4, 3DNow!, SSE and SSE2) instruction sets.
 * Supports Microsoft macro assembler (MASM) 5 and 6 syntax (incomplete).

Disassembler
There is an associated Watcom disassembler, wdis. The assembler does not have listing facilities; instead the use of wdis for generating listings is recommended. wdis can read OMF, COFF and ELF object files and PE and ELF executables. It supports 16-bit and 32-bit x86 instruction set including MMX, 3DNow!, SSE, SSE2, and SSE3. Support for PowerPC, Alpha AXP, MIPS, and SPARC V8 instruction sets is also built in.

JWasm
JWasm is a fork of Wasm originated by Japheth with following features: Japheth ceased development (or rather, was out of contact) of JWASM in January 2014 with version 2.12pre, but others on the Masm32 forum picked up where Japheth left off.
 * Native support for output formats Intel OMF (16/32-bit), MS Coff (32-bit and 64-bit), Elf (32-bit and 64-bit), Bin and DOS MZ.
 * Precompiled JWasm binaries are available for DOS, Windows and Linux. For OS/2 and FreeBSD, makefiles are supplied.
 * Supports Intel x86 (8086, 80186, 80286, 80386, 80486, Pentium, Pentium Pro), x86-64 instruction sets with SIMD (MMX, 3DNow!, SSE, SSE2, SSE3 and SSSE3, SSE4.1/2 (since Jwasm), AVX (since JWasm 2.06), VMX (Intel VT-x; AMD SVM, the latter though already implemented, currently still inactive) extensions (since JWasm 2.09)).
 * JWasm is written in C. The source is portable and has successfully been tested with Open Watcom, MS VC, GCC and more.
 * On Windows, JWasm can be used with both Win32Inc and Masm32. Since v2.01, it will also work with Sven B. Schreiber's SBS WALK32 Win32 Assembly Language Kit
 * C header files can be converted to include files for JWasm with Japheth's own dedicated h2incX.
 * JWasm's source code is released under the Sybase Open Watcom Public License, which allows free commercial and non-commercial use.
 * Fully supports Microsoft macro assembler 6 syntax, all MASM 8 instructions sets.

HJWasm
HJWasm, adding the prefix H in reference to Masm32 forum member Habran who started off this second WASM development continuation. Version 2.13pre was originally announced in 2016. New features include:
 * Instructions:
 * SIMD:
 * MMX: MOVQ and added in 2.13, to supplement MOVD.
 * AVX2: VGATHERDPD, VGATHERQPD, VGATHERDPS, VGATHERQPS, VPGATHERDD, VPGATHERQD, VPGATHERDQ, VPGATHERQQ, VEX-encoded general purpose instructions added in 2.13. Remaining instructions added in 2.16.
 * AVX-512: VCMPxxPD, VCMPxxPS, VCMPxxSD, VCMPxxPD, VCMPxxSS, AVX-512F set, EVEX-encoded instructions added in 2.13; VMOVQ added 2.13, to supplement MOVD. Remaining instructions added in 2.16.
 * Random Number Generator: RDRAND, RDSEED added in 2.13.
 * half-precision conversions: F16C(VCVTPH2PS, VCVTPS2PH) added in 2.13.
 * Intel MPX: Added in 2.31.


 * Registers: RIP, ZMM registers added in 2.13.
 * OO language extension added in 2.25.

HASM
HASM is a renamed version of HJWASM, starting in version 2.33. The name was used following a MASM Forum discussion thread that originally proposed a replacement name. The name HASM was proposed by forum member habran in Reply #6, and was finalized at the end of discussion thread at Reply #33. No known features are added in HASM's release cycle.

UASM
The name was actually used in version 2.33 (dated 2017-05-20) at Terraspace ltd's product page, but it was only announced in version 2.34. Changes to HJWASM includes:
 * Instruction sets: RDPID added in 2.38.
 * AVX-512: VAESDEC added in 2.38
 * Data transfer: MOVBE added in 2.47. MOVABS added in 2.48.
 * Intel ADX: ADCX, ADOX added in 2.38
 * Intel MPX: Support of BND prefix added in 2.34. BND prefix removed from JCXZ instruction group in 2.40.
 * CLMUL instruction set: Added in 2.46.8, including pseudo-op forms of CLMUL.
 * Hashing: SHA instruction set added in 2.46.8.
 * Supervisor Mode Access Prevention: CLAC added in 2.38.
 * Persistent Memory Extensions: CLFLUSHOPT added in 2.38.


 * Addressing modes: 64bit absolute immediate (2.37)
 * Identified types
 * Record types: fully supports registers and up to 32bit record fields in 2.41.
 * Support for 128bit: Added in 2.42, inline declaration with the type added in 2.43.1 / .2.
 * Support of typedef chain on return types added in 2.46.8.
 * m512 built-in types added in 2.47.


 * Console colour coding: Added for Windows, OSX and Linux in 2.43.1 / .2.
 * Function calling: C-style function calling added in 2.46.