Best solution for cross-platform games?

What are some of the better solutions for dealing with cross-platform games in the three areas of input, sound, and networking.
There is, of course, SDL; however, I was hoping to find a free source solution using a license like Haiku (MIT, BSD, or public domain). There is Allegro, but I'm not sure what to make of the donationware license.
Are there any such libraries out there? If not for all three, maybe one of the items like just sound or just input?
...or would specifically coding these three areas for each OS be the better solution?