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.
GeekOS is a tiny operating system kernel for x86 PCs. Its goal is to be simple enough for beginners to understand and modify, but realistic enough to be interesting and fun. The primary development environment for GeekOS is Linux or Windows using gcc, nasm, and the Bochs PC emulator.
The HLA Standard Library was developed to support the High Level Assembler (HLA), but could be used with other assemblers or higher-level languages if the necessary headers were developed. It supports 32-bit versions of Windows, Linux, Mac OS X, and FreeBSD, and is written entirely in HLA. It includes the following modules: args, arrays, bits, chars, console, conversions, cset, date, environment, exceptions, file class, file I/O, filesys, lists, math, memory-mapped files, patterns, RNG, stderr, stdin, stdout, strings, tables, time, timer, zstrings, sockets, threads, and blob. An automated test suite is included.