Different keys are compatible under different circumstances dude. There aren't really any programs that will help you there, except for maybe mixing in fifths (Or +1 / -1 on the Camelot wheel... which is honestly easier to remember). It will tell you that mixing up a semi-tone will create clashes if both melodies are layered, but can create a 'rising' feeling if you remove one melody line and introduce the next... Which is still mixing in key.
Best bet... Sort by key, Keep your music well organised into Categories, or properly tagged to narrow down with search.
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