Solar Assembler
Solar Assembler (aka Sol_Asm) is a multipass macro assembler written by Bogdan Ontanu. It supports HLL primitives, like procedures, structures/unions, .IF/.ENDIF, .REPEAT/.UNTIL, etc. Sol_Asm can produce binary files, PE executables (32/64-bit), COFF object files (32/64-bit), ELF object files (32-bit only) and Mach-O object files (32-bit only).