Assembler for MCS-51 compatible Microcontroller

• ASEM-51, by W.W. Heinz, is a free 8051 macro assembler for MS-DOS, Windows and Linux version 1.3
  
• ML-ASM51 MetaLink's 8051 family macro assembler.
  
• A51 PseudoSam 8051 Cross Assembler, V1.4.09
  
• AS31 C source for an 8051 assembler, and a simple monitor from Ken Stauffer.
  
• MCS-51 Assembler and Disassembler V4 a nice MCS-51 tool for windows By Controllertechnik