Two brokerages, one that was required for stock options I think, but I still use because they offered a Solo Roth 401k.
Four mutual fund companies, covering funds that were not offered, had transaction fees, had higher minimums, or were closed at my main brokerage.
One company 401k that I'm slowly rolling over into an IRA. I have to liquidate to cash in order to roll over, so I don't want to do it all at once and be out of the market for over a week.
One HSA manager for our HSA accounts, which I'm treating as a Roth equivalent.
Multiple accounts at all institutions, hers, mine, and ours, and the mutual fund companies usually assign an account number to each mutual fund held there.
All tracked in Quicken, so while it's not something I intend to continue forever, it's not hard to follow now.
ETA: Two online banks and one brick and mortar bank and one credit union.