simavr is described as 'new AVR simulator for linux, or any platform that uses avr-gcc. It uses avr-gcc's own register definition to simplify creating new targets for supported AVR devices'. There are six alternatives to simavr for Linux and Windows. The best alternative is SimulIDE, which is both free and Open Source. Other great apps like simavr are Oregano (Free, Open Source), proteus VSM (Paid), SimulAVR (Free, Open Source) and Emulino (Free, Open Source).
SimulIDE is a simple real time electronic circuit simulator. It's intended for general purpose electronics and microcontroller simulation, supporting PIC and AVR. PIC simulation is provided by gpsim and avr simulation by simavr.
The SimulAVR program is a simulator for the Atmel AVR family of microcontrollers. (ATtiny and ATmega) SimulAVR can be used either standalone or as a remote target for avr-gdb. There is a python- and TCL interface.
PICsim emulates a microcontroller PIC16F628/16F777/16F877A/18F452/18F4550/18F4620 and periferics such as USART and timers, the simulator architecture permit easy implementation of external elements in c language.