U2 - Salome

In the winter of 1990, U2 were hard at work in Hansa Ton recording studios in Berlin, Germany. The ultimate result of this effort would be the November 1991 release of their next album, Achtung Baby. However, in December 1990 that album was a great ways off, because U2 (unlike most other bands) entered the studio with very few lyric or song ideas.
Instead, U2 came into the studio to create as well as record. Here they sought inspirations for songs from playing together. They would etch out ideas while improvising around some basic idea, or riff. Since all this jamming was taking place in a recording studio, even the simplest of ideas was captured on tape. The highlights of these tapes were then edited down and compiled into "working tapes" recorded onto DAT (Digital Audio Tape) cassettes. Tapes of this nature were used to hold possible song ideas, as well as a means for Brian Eno (and others) to hear the band's progress and make suggestions about the music.
In April of 1991, it was announced that the tapes had found their way into the hand's of bootleggers. Since then, the U2 working tapes have been pressed in a variety of forms:
May 1991: The New U2: Rehearsals and Full Versions
The debut pressing of the sessions. Available on vinyl only, as two separate double album packages. The covers were identical except for the colors of the lettering. One cover featured silver lettering, while the other had gold. In this pressing both LP's of the silver lettered album proved to be identical. This resulted in four LP's being released, but with only three LP's worth of material.
June 1991: The New U2: Rehearsals and Full Versions
It was widely rumored that the set had been pressed again, but this time without any duplication between the LP's. If true, this meant that there were now four LP's worth of material available.
November 1991: The New U2: Rehearsals and Full Versions
This time the pressings were released as a boxed set of 5 LP's. Surprisingly, there was no duplication within the set. All of these LP's were pressed on translucent vinyl, in either blue or green (pink pressings have also been rumored). There were now 5 LP's worth of material available, which came to a staggering total of 3 hours, 27 minutes, and 28 seconds.
February 1992: Salome: The [Axtung Beibi] Outtakes
This was the release that had been deemed "too hot" to ever be pressed. The complete three and half hours worth of material were now available as a triple compact disc set. Since these CD's were mastered from the original DAT recordings, there's no quality loss between the original working tapes and these CD's. Thus the sound quality is far superior to the LP's. The title (Salome) is believed to have been a working title used during the Achtung Baby sessions, but it's not clear which song it was refering to.
With these releases U2 found themselves in the dubious position of being:
"the first major band to have studio sessions released before the finished product was either released, abandoned or the group broke up".
U2's manager Paul McGuiness reacted to the bootlegs by releasing a press statement accusing the bootleggers of cheating the fans by passing off inferior material. He also stated that the finished product had evolved by leaps and bounds from what was being illegally circulated.
Regardless of the superior polish of the finished material released as Achtung Baby, the material found on the bootlegs is fascinating in and of itself. The most compelling aspect of the bootleged material is that, rather than offering slightly alternative versions of tracks found on the finished record, they instead reveal the songwriting process itself. Familiar solos, bass lines, bridges and riffs abound, and there is also a host of interesting songs that didn't find their way onto Achtung Baby.

Disc 1:
Salome (Version 1) (5:57)
Where Did it All Go Wrong (Version 1) (4:03)
Where Did it All Go Wrong (Version 2) (3:42)
Heaven and Hell (6:44)
Doctor Doctor (2:35)
Jitterbug Baby (3:55)
Got to Get Together (9:14)
Salome (Version 2) (5:28)
Here Comes The Sunset/Chances Away (14:57)
Chances Away (Short Segment) (1:40)
I Feel Free (Version 1) (6:35)

Disc 2:
I Feel Free (Version 2) (4:31)
Sweet Baby Jane (2:02)
Who's Gonna Ride Your Wild Horses (Version 1) (5:35)
Who's Gonna Ride Your Wild Horses (Version 2) (4:00)
Who's Gonna Ride Your Wild Horses (Version 3) (4:09)
Take Today (Instrumental) (5:31)
Even Better Than The Real Thing (Instrumental) (6:29)
Blow Your House Down (Version 1) (4:51)
Blow Your House Down (Version 2) (7:44)
Laughing In the Face of Love/So Cruel (Version 1) (7:38)
Wake Up Dead Man/Blow Your House Down (Version 1) (5:33)
Take Today (Vocals) (6:32)

Disc 3:
Calling Out to Someone (1:05)
Laughing In the Face of Love/So Cruel (Version 2) (3:11)
Acrobat (4:19)
Salome (Version 3) (5:56)
Who's Gonna Ride Your Wild Horses (Version 4) (5:09)
Wake Up Dead Man (Mix Version) (5:16)
Unnamed Instrumental (5:35)
Salome (Version 4) (3:50)
Salome (Version 5) (13:06)
Salome (Version 6) (5:58)
Salome (Version 7) (8:04)
Salome (Version 8) (12:03)