Natural Worlds will immerse you in a bird sanctuary, a thunderstorm, a night-time forest with crickets and owls or anything else you can imagine!
Natural Worlds also has a built-in world editor allowing you to modify or create your own unique worlds from scratch. You can add up to 50 environment sounds to each world. (If that's not enough, let me know).
To help eliminate repetition, environment sounds can be grouped together so only one sound within each group plays at one time (think of a group as one "meta-sound" with different variations within it).