is a website for a book by Nancy Howland-Walker. The book is titled "Instant Songwriting - Musical Improv from Dunce to Diva" (publ 2012)
The book is a detailed course in learning to sing improvised songs. Several "song structures" are explained, there are chapters about melody, lyrics, rhyming, motifs etc. Nancy covers well-known simple structures such as verse/chorus and tagline song, but also introduces the term "Sondheim" to the musical improv vocabulary.
The site offers a really large collection of sing-along training tracks for various kinds of song structures.
Highly recommended for all those who get to improvise a song from time to time.