Hammerhead Rythym Station is not the prettiest, but it's free beat making software that makes drum patterns quick and easy. It is an especially useful production tool for DJs, and is available for download on Mac and PC. Mixxx is extremely popular free music and beat making software. The app available for iOs (iPhone and iPad) and Android devices. Songbook lets composers plan and practice sheet music at home or on the go, complimenting the computer software. The MuseScore Songbook app is also available for download at a minimal cost. MuseScore offers a paid upgrade version, but the free software has many useful features to start writing and producing songs. Composers and songwriters might recognize this approach to musical notation from popular software like Sibelius and Finale. A minimal understanding of reading and writing music is needed, and it's free to play around with. Want to record real strings, guitar, or drums? Beat makers can easily create and print parts for studio sessions with collaborators.
This is awesome for producers who want to write sheet music for studio musicians. You can write in the notes, or use a midi controller and MuseScore will automatically write the music.
Beat makers will enjoy composing percussion, strings, and guitar tabs with ease. MuseScore is free and open source music notation software for Mac and PC.