No, there is no software because each robot is different, so each robot will require diferent equations. But as long as you have the equations you can peform simulations using MATlab(high level but more difficult) or excel(low level but easier) or by programming.

In order to find the equations get a book of Mechanics(I also recommend MITOCW) and you will get the physics background. For example how to calculate force, torque and momentum. However, physics books usually study systems with only one or two bodies. You are building a hexapod so you have (6 legs) x (at least 3 bones per leg) +(main body)= at least 19 bodies. In order to calculate the precise optimal position of the system(robot) you will need a set of matrices(one for each leg). Hence you need to know Linear Algebra(Specially to undertand the concept of linear tranformation and eigen values/vectors for solving diff. equations). You can also try a mechanical design book(in my university the class is called Dynamics of Mechanisms for Mechatronics).

By doing that you will get the perfect robot. You can use trial and error or copy someone's else design, but then I cannot garantee 100% efficiency. Articulated robots (like robotic arms, legs, insects, humanoids) require way more mathematical background than the usual 2 wheeled robot that anyone can make. If want an hexapod, you must do some maths. If you want a good eficient hexapod, you need heavy maths. That is why you dont see a many of them, people dont like maths (not to mention they are expensive).

EDIT: I forgot to mention that I might partially help you with the maths, like I always do in this board.