Among five friends, $A$ is heavier than $B$, $C$ is lighter than $D$, $B$ is lighter than $D$ but heavier than $E$. $D$ is not the heaviest. Who among them is the heaviest?

Let's analyze the given conditions step-by-step:
1. $A$ is heavier than $B⟹A>B$
2. $C$ is lighter than $D⟹D>C$
3. $B$ is lighter than $D$ but heavier than $E⟹D>B>E$

Combining these relations, we get that $D$ is heavier than $B$, $C$, and $E$ ($D>B$, $D>C$, $D>E$).
Since we are given that $D$ is not the heaviest, the only remaining person who can be heavier than $D$ is $A$.

Therefore, $A$ must be the heaviest among all five friends ($A>D$).