The Quick C-- compiler is an experimental implementation of the C-- language. C-- is intended to be a "portable assembly language" that can be used as a target language by compiler writers. C-- features a simple C-like core and support for garbage collection and exception handling.
The Amazing Awk Assembler (aaa) is a primitive assembler written entirely in awk and sed. It is quite slow, the input syntax is eccentric and rather restricted, and error checking is virtually nonexistent, but it does work. Furthermore it's very easy to adapt to a new machine, provided the machine falls into the generic "8-bit-micro" category.
Flat Assembler is a fast and efficient self-assembling 80x86 assembler. It supports x86 and x86-64 instruction sets with MMX, 3DNow!, SSE up to SSE4, AVX, AVX2, and XOP extensions. It can produce output in binary, MZ, PE, COFF, or ELF format. It includes powerful but easy-to-use macroinstruction support and does multiple passes to optimize the instruction codes for size. It is written entirely in assembly language.
J51 is a Intel MCS51 emulator with all the standard integrated peripherals. A disassembler with an integrated debugger is also included. Standard peripherals emulated are Timer 0/1 (Mode 0, 1, 2, and interrupts), serial interface in polled and interrupt mode, standard I/O, and ports 0 to 4. Microprocessors emulated are the Intel MCS 8051 (no peripherals), Intel 8051, Intel 8052, Philips LPC674, and Philips LPc900.