This is not a good platform for just browsing for alternative software. Recommending a piece of software for a certain task is inherently different that suggesting alternatives to a known piece of software. I suggest that this site will work reasonably well for the former but very poorly for the latter.
The most obvious case is looking for "alternative to X on platform Y". The classic case of this has apparently already been asked:
iTunes alternative on Ubuntu
This is a really bad fit for this format because there is no specific problem to solve. This is a basic database lookup query, not a call for expertise. Worse, this question has no scope that would make the choice of a specific music player over another beyond the reasons everybody else used to pick a player. In short the best answer to this question is the most popular music manager apps for Linux. This not a question you need to pose to experts, it is a poll. As it turns out there is a site that does that pretty well. It's called –get this– alternativeTo!
Note it's results for alternatives to iTunes for Linux. Given the lack of criteria or problem to solve, this is all the answer that question calls for. It is a database query on possible alternatives sorted by popularity.
If this sort of question is to be allowed, this site will not add anything meaningful to the internet. Let's save our question space for problems that need solving and specific criteria that aren't immediately apparent without a little expertise in the field.
Disclaimer: I have no vested interest in AlternativeTo.net, I just think this format of question should be left to databases that are set up for this sort of cross referensing instead of hoisting it on the QnA format here.