I have a substantial spreadsheet (20+ sheets) that tracks all my financial life: net worth over time, expenses, taxable lots positions and loss harvesting opportunities, RSU vesting, investment returns, projected passive income and 1040 tax approximations, ideal portfolio allocations and rebalance thresholds, taxable equivalent yields for municipal bonds, safe withdrawal rates approximations, buy vs rent calculations under different tax regimes and interest rates, …

I built that incrementally over 10+ years out of necessity. No other tool I ever tried (Mint, Personal Capital, ...) has been as reliable, flexible, transparent and thorough.

I currently keep it manually updated once every month or two (and clearly use formulas such as GOOGLEFINANCE() as much as possible), it takes about 10mins to iterate over all the sheets and align them with the transactions of my various bank/brokerage accounts, so I can get the latest snapshot of my finances, and once a year I do a more thorough check to make sure nothing is missed and all numbers match to the penny. I find that time investment extremely well worth it. In a weird way, knowing that I'll have to eventually manually report any transaction on my sheet serves as a deterrent to not generate too much activity on my brokerage accounts, which is almost always better than the alternatives :-)

One day I might decide to convert it to a little SaaS and see if anyone would pay money for it. Probably not but it would be a fun exercise so I could add automatic scraping of bank/financial accounts.