In TheoryTab Database I can enter chords stepwise and then find the songs that share the same sequence. Great tool for testing if I accidentally ended up with a melody close to an already published song.
However, you have to start with a fixed key like C, then repeat for C#, D, D# etc. 12 times to find all songs in the database with the same sequence, if you want to check for transpositions too. So why not make it possible to search with chord degrees instead, i.e. using I, V, vi, IV etc. Or alternatively make it possible to get answers for transpositions of the sequence too without having to type the sequence again.
This method requires you to listen to a lot of songs and check for similarity. Thus it would be much better if you could check directly for similarities with other songs in the database. E.g if I enter my melody in Hookpad with scale degrees, it could be possible to check for close matches with existing songs. Albeit this solution will require much more work on behalf of the programmers to implement.
I guess most of us are afraid to accidentally copy another song?