* Sirius Black's "execution": Sirius was wrongly convicted of murdering 12 muggle people and sentenced to Azkaban. He was presumed dead, but he was never actually executed.
* Peter Pettigrew's "execution": Peter was sentenced to death for the murders that Sirius was framed for. However, he staged his own death and escaped, so he was never actually executed.
* The execution of the Death Eaters: During the Battle of Hogwarts, many Death Eaters were captured and presumably would have been executed. However, the exact fate of these Death Eaters is never explicitly stated.
It's important to remember that the wizarding world, unlike the muggle world, has a different legal system and the concept of execution is not as clear-cut.