Although not visually attractive as other biosimulatores (it´s not 3D), the amount of information this program provides is amazing, once a user is able to interpret the genetic information of the virtual microrganims evolving in front of him. I tried all the free options available under windows, and this the one I prefer. You have lot of options to play with (although I personaly don´t like to interfere in a world once I established the inicial conditions), the organisms are just made of DNA segments colour-coded that evolve "plant", "animal" or "mixed"-like behaviours (I mean the type of metabolism) , with predators emeging after some turns and engaging in a fight with their preys. More complex organisms also are going to arrive as the time goes on. All in all, an extremely rich artificial life program with an active development team. Be sure to read the user manual in order to understand the basic concepts of tthe program.