Another, simple for some complicated for those brought up in a monotheistic mindset, idea is one of Duality. One entity controls that which is evil and another that which is good. In my faith there is a god that created the physical/mortal world and another, pure god that embodies good virtues and the soul.
Christianity tries to do a similar job with their aspect of a god and his lesser counterpart satan, but falls short because the god is supposed to be completely omnipotent thus allowing something 'evil' like satan to exist is at the very least inane.
Another problem with the Christian experience is lopping everything into 'free will' or 'agency' which does wonder for murderers and burglars but falls short in the realms of locusts and guinea worms.
This predicament is further hampered by concepts like predestination, predetermination, 'everybody goes to heaven,' and other divine plans. If a person's actions or life has been predetermined, even in the most slight of contexts, then the presiding god would know of such 'evil' outcomes and continue to let such outcomes occur. This means either 1. god is uncaring, 2. god is not omnipotent, or 3. god uses some people as examples.
A final thought has more of a metaphysical than theological base: good and evil are simply fluid, complementary concepts. The old adage 'Yin without Yang' and 'there can be no good without evil' apply here. Specifically, the concepts of 'good' and 'evil' are fluid and based on morays, ethics, and taboos.
The Problem of Evil exists, has always existed, and will most likely always exist, unfortunately.