If you are using Linux and want a free IDE for your 8051 microcontroller, then you can use this. MCU 8051 IDE is integrated development environment for microcontrollers based on 8051. This IDE supports assembly and C languages programs. It has its own Assembler and C complier. SDCC is used as the C compiler.
This IDE contains simulator, source code editor, assembler, HW programmer and much other tools. Simulator supports over 79 MCU primarily from Atmel
HW programmer supports 8 ISP programmable MCUs from Atmel (AT89Sxx, AT89LSxx).
There is also support for simple hardware simulation (like LEDs, keys, etc.).
Sample Screenshot:

Features of MCU 8051 IDE:
- Editor with syntax highlight and validation
- 8051 Assembler
- 8051 Disassembler
- 8051 Simulator
- Project management
- Custom editable commands (using shell scripts)
- Dynamic help for instruction at the current line
- Hexadecimal editor for eXternal RAM and Code memory
- Scientific calculator
- Graph showing voltage levels on ports
- Advanced text editor for TODO list
- Register watches
- Export to XHTML and LaTeX
- Conversions between IHEX8 and Binary
- Command line interface
- Editor command line
- Embedded filesystem browser
- Popup-based completion
- Backward stepping
- Autosave
- UNIX manual page
- 8051, 80C51, 8052, AT89C2051, AT89C4051, AT89C51, AT89C51RC, AT89C52, AT89C55WD, AT89LV51, AT89LV52, AT89LV55
- Support for C language
- Many other things ...
Download the IDE from here
For more details visit here
Tags: linux 8051, 8051 ide, 8051 linux ide, at89s51