You can download UVI51 from:
www.dte.uvigo.es
UVI51 is a multi-micro simulator, that is, you can simulate a system with up to four 8051s interconnected, ... and external peripherals too.

UVI51 also includes an assembler and a logic analyzer. The version you can download is limited to 500 lines in the source code, but I can send you a more powerful version (free, of course) if you need it.

UVI51 is an MSDOS application, but you can run it from Linux (dosemu) or Windows.

Regards,
Alfredo del Rio.