There are several animals that can be mixed together but just like a community fish tank there are no guarantees. When mixing animals think about the space that each requires, and think about the niches each fills within the environment. for instance a day gecko and anole are both aboreal and diurnal, not a good combination, an anole an a house gecko, on the other hand are active during different times and thus have different niches. A snapping turtle and tokay gecko for example would avoid each other pretty easily, a snapping turtle and a water dragon, would not. Also consider food agression, if all the members of your tank are cricket eaters, you can bet that feeding struggles will occur.