Simple crossplatform IDE for NASM, MASM, GAS and FASM languages
An x86 assembler that aims to be compatible with MASM and TASM
Keystone assembler framework: Core (Arm, Arm64, Hexagon, Mips, etc.)
Japheth's assembler, JWasm
miniasm is a short bytecode based assebler, interpreter and compiler
Visual MASM - Assembly IDE for Microsoft MASM