IBM was the other offer on the table. Scott managed to scuttle the deal but his ability to do so was far from a certainty since he was already out as CEO.
Google was pretty much incompatible, they had no interest in workstations or paying for quality as their focus was redundant arrays on inexpensive machines.
Fujitsu was the best actual option for commercial compatibility, but everyone felt it would be a waste of time to pursue that as the USG would almost certainly block a foreign sale.
Google bought Motorola, amd that went okay until Samsung blew its top. Recall this was the era Google was frantically buying IP to shore up it's patent portfolio. Apple had gone "thermonuclear", so a somewhat-independent Google-ow ned Sun was in the realm of possibility,perhaps to be sold piecemeal.
Although Sun and Fujitsu had a long-standing business and development relationship, I think it would also have been problematic from a strategy and cultural perspective. My observation with the 3 big Japanese computer companies (NEC and Hitachi being the others) in the 2000s is that they aspired to be major global computer system suppliers--but weren't willing to actually make the investments to make such a thing possible.
I didn't think at the time that IBM was a good fit. I'm not so sure now in retrospect--though they would have had to rationalize the Unix business in particular.
That would have been instead of the NeXT merger which brought Jobs to Apple.
It seems likely a Sun-Apple would have ended up with both companies destroyed, and Steve Jobs might have spent the early 2000s hawking enterprise web dev software like he was doing at NeXT in 1995.
Probably Google with Android. They were working on it at roughly the same time as Apple but released it later. This interview with Chet Haase on the CoRecursive podcast is an interesting account of those years:
My supposition has been that, absent Apple to throw their weight behind the iPhone, someone would have created a pure touchscreen device (Android had one such concept under development IIRC) but it would have failed because it would have been just one phone among many, gathering dust at retail stores.
Apple bet the farm on one phone, had the built-in fan base to leverage, and the resources to make it work well from day one.
Though it was a factor -- it's real success was that it was OS X in a tiny phone -- basically a portable Mac with totally wireless connectivity. For many applications you could simply leave your laptop at home and walk on the bus and go on with your day.
Steve Jobs even said at its launch that the iPhone rans OS X and ran "desktop class applications". This with it's multi-touch full screen keyboard and GUI integration meant that people could interact with it much more naturally than any phone in the past. Even my mother could use it, which is remarkable, considering how many cell phones I gave her that she couldn't use.
I guarantee you that the most used features from day one of the iPhone launch were: Safari, Google Maps, and YouTube, with the Music app being simple a "nice to have".
At least it seems oracle's stewardship of java is good enough (atm at least...).