ChordBud is described as 'all in one app that combines most important concepts when sketching a song'. There are five alternatives to ChordBud for a variety of platforms, including Mac, Windows, iPhone, iPad and Linux. The best alternative is Impro-Visor, which is both free and Open Source. Other great apps like ChordBud are Suggester (Paid), ChordPad (Paid), Melody Generator (Free) and Chord NOTE (Paid).
Impro-Visor (short for “Improvisation Advisor”) is a music notation program designed to help jazz musicians compose and hear solos similar to ones that might be improvised. The objective is to improve understanding of solo construction and tune chord changes.
Suggester is a tool to assist in the creation of songs and chord progressions. This app will help you find chords that work together. It is efficient and fun; use it to build musical phrases that will carry emotion through tension and release.
Described as chord sequencer it lets you quickly create chord progressions, play them in many styles, transpose, adjust tempo, change instruments. Great for practicing. I used it for improving my scales on guitar and I have to tell it is amazing.
This app is a random midi melody generator which you can use to create melodies. The melodies are procedurally generated and are royalty free. You are free to download the midi files and use them in your own music.