Wikipedia identifies Kazaa as the file-sharing site that became popular after Napster shut down and influenced Spotify’s origin story. Daniel Ek has described the rise of file sharing as part of the problem Spotify was designed to address: offer a legal service that was easier and more attractive than piracy while compensating the music industry.
Napster operated from 1999 until 2001, when legal action forced its original service to close. Kazaa, introduced in 2001, became one of the prominent peer-to-peer successors. It used the FastTrack network and allowed users to exchange music and other files directly.
Spotify was founded in Stockholm in 2006 by Daniel Ek and Martin Lorentzon and launched in 2008. Its early concept was not simply to imitate a file-sharing network; it aimed to combine immediate access with licensing, advertising, and subscriptions. Kazaa is therefore part of the company’s technological and cultural backdrop, not Spotify’s corporate predecessor.