Though most music composing softwares (or rather, most effective) often come with a high price tag and require some form of input device to work regardless, a major free alternative is Anvil Studio. Anvil Studio is a completely free midi composition program that allows you to compose music without any external devices - it has a very easy to use interface and produces proper sheet music as you compose, unlike many other programs which use basic composition pieces. Beginners and professionals alike can make use of Anvil Studio with great ease. It simulates all of the default Windows MIDI instruments and, once you're done with your piece, you can save the MIDI file. You can use online converters, such as the one at Hammie.net, to convert the MIDI to an MP3 or WAV file.