Stephen Stills’ first solo album is the only one with Eric Clapton and Jimi Hendrix playing new music on it. They did separate songs, though. Hendrix on “Old Times Good Times” and Clapton on “Go Back Home”.
Rosie Vela’s Zazu is the only album that both Walter Becker and Donald Fagen played on during their breakup of Steely Dan. They’re credited for some of the same songs but recorded them in separate sessions.
I’m unclear on the question being asked. Albums that an artist contributed only one song to and it appears nowhere else (songs they got the credit for)?
Hendrix’s Electric Ladyland has Steve Winwood and Jack Casady guesting, and on the same song as well.
If that’s what you’re looking for here.
I’m looking at uniqueness. The only album that… Fill in the blank with any good trivia.
The LP of Monty Python’s Matching Tie and Handkerchief is the only record I know of that has three sides.
Big Bambú by Cheech and Chong is the only album that comes with its own humongous rolling paper.
POTUS Freaked Out And Small is the only album with my name in it.
Public Image Ltd’s Metal Box came in a metal box.
Dave Mason’s Alone Together was a multicolor disc.
Later versions of these had regular packaging.
“Come on-a My House” by Rosemary Clooney is the only pop song written by a Pulitzer Prize winner (William Saroyan) and a chipmunk (Ross Bagdasarian, aka David Seville).
“Second Winter” by Johnny Winer has three sides.
So did Joe Jackson’s “Big World”. What makes it even more interesting is the fact that it consists of 15 new songs recorded live on stage, the audience was asked to keep quiet during the songs.
Led Zeppelin
Led Zeppelin III had a pinwheel thingie on the cover
Their last album “In Through the Out Door” originally came wrapped in a brown paper bag and had various cover pictures.
ELO’s “Out of the Blue” came with a cardboard cutout that you could assemble the cover spaceship on.
Rolling Stones
The original “Sticky Fingers” had a cover designed by Andy Warhol and had a functioning zipper
The original “Some Girls” had pictures of Lucille Ball, Farrah Fawcett, Judy Garland, Raquel Welch, and Marilyn Monroe till they or their respective estates sued. Then all the removed pictures said “This space available” and finally was released with the various members of the band wearing women’s wigs.
XTC’s “English Settlement” had a single-disc and double-disc release
I’ll try and think of interesting guest players on albums yet for now could only think of the covers.
I figured this was gonna bite me in the butt. Matching Tie and Handkerchief has two grooves on one side of the LP, in effect giving it three sides on one disk.
I didn’t get a cardboard spaceship. 
“A Toot and a Snore in '74 is a bootleg album consisting of the only known recording session in which John Lennon and Paul McCartney played together after the break-up of the Beatles in 1970.”
Millions of fans dreamed of such a reunion, so why is this one-of-a-kind recording not better known? Mostly because the drug-fueled session was a dud.
The four CD album “Zaireeka” by the Flaming Lips is unique. The four CDs are intended to be played simultaneously on four stereo systems to produce the final sound. I’ve always wondered if anyone who bought that album ever did so successfully. Who has four systems and most importantly, can exactly sync them?
I’ve posted this elsewhere on the board.
20/20 is the only Beach Boys album to employ the creative input of 4 convicted murders.
Charles Manson is the uncredited cowriter of “Never Learn Not to Love”
Phil Spector cowrote “I Can Hear Music”
Huddie (Lead Belly) Ledbetter wrote “Cotton Fields”
Jim Gordon was a (Wrecking Crew) session drummer.
According to Wikipedia Innuendo the track from the Queen album of the same name has Steve Howe of Yes playing some flamenco style guitar. This is supposedly the only time a Queen album has some guitar playing by someone other than the members of Queen.
TCMF-2L
Just a guess here – The Rolling Stones’ Sticky Fingers is the only album that has a working zipper on the cover.
ETA – I think Family Style is the only album which has songs that both Stevie Ray Vaughan and Jimmy Vaughan collaborated on.
I don’t know if there is another studio album Jimmy played on, but at least on “Live At Carnegie Hall”, Jimmy joins Stevie Ray on stage. I seem to remember also on a few tracks on “Live Alive”, but I’m not totally sure about that.
ETA: looked it up on wiki. Yes, Jimmy plays on four tracks on “Live Alive”.
And, I think, it may be the only time a member of Yes guested on another band’s album while they were still in Yes.*
And on a related point, the Yes album Drama was the only time an active band completely absorbed another active band to make a new band. (Wouldn’t be surprised if someone proves me wrong but let’s see…)