MCU 8051 IDE
This IDE contains simulator, source code editor, assembler, HW programmer and much other tools. Simulator supports over 79 MCU primarily from Atmel.

8051 Development Tools by Chin-Shiuh Shieh
Assembler, Simulator, Programmer, Debugger, C Compiler, BASIC Compiler, Pascal Compiler, Disassembler and Terminal Emulator.
BASCOM-8051 is the Windows BASIC COMPILER for the 8051 family and BASCOM-AVR is the original Windows BASIC COMPILER for the AVR family.