It simulates Input / Output ports, interrupts, timers, USARTs and all other peripherals present on each supported processor. Proteus also has the ability to simulate the interaction between software running on a microcontroller and any analog or digital electronics connected to it. The suite combines mixed mode SPICE circuit simulation, animated components and microprocessor models to facilitate co-simulation of complete microcontroller based designs. Proteus is a Virtual System Modelling and circuit simulation application.
The application is a great alternative for Virtual System Modelling. You can simulate a single processor or multiple ones at the same time.
Proteus is a great electrical suite for circuit simulation purposes.