checking the simulator:
$ simulavr -L
at90s1200
at90s2313
at90s4414
at90s8515
atmega8
atmega16
atmega103
atmega128
at43usb351
at43usb353
at43usb355
at43usb320
at43usb325
at43usb326
starting the simulator server
$ simulavr --device atmega8 --gdbserver
Simulating a atmega8 device.
devsupp.c:338: MESSAGE: TODO: attach IO Reg 'TWBR' at 0x0020
...[ lots more like this ]...
avrcore.c:475: MESSAGE: attach: Internal SRAM from 0x0060 to 0x045f
decoder.c:3875: MESSAGE: generating opcode lookup_table
main.c:415: MESSAGE: Simulating clock frequency of 8000000 Hz
Waiting on port 1212 for gdb client to connect...
now simulavr is ready to simulate an atmega8 and is waiting for a client to connect on TCP port 1212.
in the following example, the “stdiodemo” test elf from the avr-libc examples is used, and I started programs from within the base of the avr-libc examples dir.
avr-ddd --debugger $AVRROOT/bin/avr-gdb

(gdb) file stdiodemo/stdiodemo.elf

(gdb) target remote localhost:1212
Remote debugging using localhost:1212
0x00000000 in __vectors ()

(gdb) load
Loading section .text, size 0x147c lma 0x0
Loading section .data, size 0x74 lma 0x147c
Start address 0x0, load size 5360
Transfer rate: 2858666 bits/sec, 184 bytes/write.

(gdb) break stdiodemo.c:53
Breakpoint 1 at 0xce: file stdiodemo.c, line 53.

(gdb) step
Single stepping until exit from function __vectors,
which has no line number information.
0x00000064 in __init ()
(gdb) continue
Continuing.
Breakpoint 1, main () at stdiodemo.c:58

a screenshot showing the registers window:

a set of screenshots showing avr-ddd and simulavr’s display window.
the binary loaded into this version is a much simpler assembly program chosen to illustrate the simulavr display window. in the avr-ddd screenshot, I’ve marked the instruction that the debugger has just executed and the associated define, showing that it has just set the r16 register to 0xFF. in the simulavr display window screenshot, I’ve marked the section showing how the r16 register field reflects this change.
admittedly, this is not not terribly impressive, but it does show that the applications have the potential for practical use.