Red Hot Chili Peppers is a popular american rock band founded in 1983 by vocalist Anthony Kiedis, bassist Michael "Flea" Balzary, guitarist Hillel Slovak and drummer Jack Irons. Over the band's career, there have been many songs that have yet to be released, either partially or completely.
One Hot Minute (1995-97)
One Hot Minute is the band's seventh album released in 1995 and was the band's first album without guitarist John Frusciante (who left in 1992) and is their only album with Dave Navarro (from Jane's Addiction). Twenty one songs were recorded during the One Hot Minute Sessions and thirteen of them ended up on the album, one (Melancholy Mechanics) would end up as the Japanese track on the Japan release of the album, three (Let's Make Evil, Stretch You Out, Bob) would end up as three iTunes tracks in 2006 and one ended up as a B-Side on the My Friends single. A cover song "I Found Out" was recorded but ended up on the John Lennon tribute album "Working Class Hero: A Tribute to John Lennon" also released in 1995. The songs that weren't released are Blender, The Intimidator and Slow Funk. Blender was one of two songs that were dropped from the album at the last second (Stretch You Out being the second one, it would be a B-Side on the My Friends single).  Some of the songs that were dropped from the album had working titles and it's unknown if Blender, The Intimidator or Slow Funk were working titles.
After the tour for One Hot Minute, there was meant to be a follow-up to the album with Navarro on guitar, they went so far as to write twenty songs for the follow up but only one known song was recorded called "Circle Of The Noose", the names of the other reportedly nineteen songs remain unknown.  The album was scrapped when Navarro was fired and Frusciante rejoined the band and the recorded and released Californication in 1999. It is unknown if some of the unmentioned songs from the scrapped album with Navarro ended up on Californication. Circle of the Noose however would be leaked online on February 3, 2016.
Greatest Hits (2003-2004)
Greatest Hits was a compilation album released in November 2003 and is made of songs from Mother's Milk (1989) to By The Way (2002) and two new songs, Fortune Faded and Save The Population. However according to drummer Chad Smith in a 2011 Modern Drummer Magazine, there were sixteen songs recorded during the Greatest Hits sessions and Fortune Faded and Save The Population were two of those songs. The other songs recorded from the sessions were Bicycle Song, Runaway, Starlight and 50Fifty. Bicycle Song and Runaway would end up as iTunes bonus tracks on By The Way iTunes released. Starlight and 50Fifty would be leaked online in 2015. The names or the existences of the remaining ten songs are unknown.
Stadium Arcadium (2004-2006)
Stadium Arcadium is the band's ninth album released in May 2006 and is the band's first and (as of 2020) only double album. The album would go onto to become a massive success and many regard it as the band's best album since Californication in 1999. The band recorded a total of thirty eight songs and thirty seven of them (according to Kerrang and Rolling Stone) either ended up on the album or being B-Sides to the album's many memorable singles. It is unknown what the name of that song was or if a thirty eighth song was ever recorded.
The Getaway Follow-Up (2018-2019)
In September 2018, Anthony Kiedis announced a follow up to the band's 2016 album The Getaway with a 2019 release. The recordings were halted by the Woolsey Fire in November 2018. The band spent the rest of 2019 performing shows with the still untitled album being pushed to a 2020 release. On December 15, 2019, the band annouced on Instagram that they and their current guitarist Josh Klinghoffer had parted ways and Frusciante would return. On january 8, 2020, drummer Chad Smith annouced a new album with Frusciante, while not revealing what happen to the songs they did with Klinghoffer. Klinghoffer gave an interview with Marc Maron on the WTF with Marc Maron podcast where he revealed that the band had scrapped the album they were working on with him in favor of a new one with Frusciante. The names of the songs or how many songs were recorded or written were never disclosed.