They were Collaborators…

In 1968 the album, Super Session was released with Al Kooper, Mike Bloomfield, and Stephen Stills.If you’ve never heard this album, well you should. This gave rise to the term Supergroup, a rock music group that was comprised of members who were already famous from individual success or with other groups. Some other examples are Cream, Blind Faith, and Crosby, Stills, Nash & Young; 1970s groups Emerson, Lake & Palmer, Humble Pie, Cactus, Toto and Bad Company.
There are two albums in my collection that while they may be considered supergroups I think they fall into the category "They were Collaborators."

Willie and the Poor Boys

With Mick Jagger and Keith Richards bickering back and forth in the press during the mid-'80s (leading many to assume that the Stones were kaput), bassist Bill Wyman decided to fill up his newly acquired spare time by forming an all-star band, Willie and the Poor Boys. The group's roots lay in the series of high-profile 1983 ARMS Concerts (which raised money for multiple sclerosis research), which led to several of the tour's participants taking it a step further and laying down some tracks in the studio. Included in this stellar lineup were Wyman's Stones mates Ron Wood and Charlie Watts, as well as Jimmy Page, Mel Collins, Andy Fairweather Low, Kenny Jones, and Ringo Starr, among others, while Wyman also served as the album's producer. The resulting 1985 self-titled album was a pleasant enough set of 12 rock & roll/R&B standards. ~ Greg Prato, Rovi

The Traveling Wilburys

Reversing the usual process by which groups break up and give way to solo careers, the Traveling Wilburys are a group made up of solo stars. The group was organized by former Beatle George Harrison, former Electric Light Orchestra leader Jeff Lynne, Bob Dylan, Tom Petty, and Roy Orbison, thus representing three generations of rock stars. In 1988, the five (who had known each other for years) came together to record a Harrison B-side single and ended up writing and recording an album on which they shared lead vocals. It turned out to be a way to transcend the high expectations made of any of them as individuals, and a delighted public sent the album to number three, with two singles, "Handle With Care" and "End of the Line" hitting the charts. Unfortunately, Orbison died of a heart attack only a few weeks after the album's release.
Two years later, the remaining quartet released a second album, inexplicably titled Vol. 3. Although it didn't match the success of the first Wilburys album, it was another million-selling hit. Throughout the '90s, there were rumors of another Traveling Wilburys record in the works, but no new albums from the group surfaced. ~ William Ruhlmann, Rovi
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