Facebook: nothing else has the network effect.
Google Drive: online documents are really convenient
Google Voice: what else has seamless integration with either android or ios.
Amazon: Buying household items like toilet paper, dishwasher detergent, etc, saves me a ton of time.
Google Drive: Dropbox, Box, OneDrive....
Google Voice: Depends what you're using it to do. Amazon & Microsoft have apps you can use that do similar tasks. Whichever you use does require access to a lot of personal data to be useful though, no matter what company you pick.
Amazon: Target, Walmart, Jet, etc... Lots of competition here. Amazon's online experience is typically better but their is plenty of competition & they often have cheaper prices. FYI in case any Target person reads this. Your site is terrible & full of bugs.
Voice is probably the hardest one to replace all 4 of them on.
For Facebook's network effects, I mentioned Twitter which is not one of the four. I did mention that my main use I've replaced with Google Photos. I did that because it's free & great. If I hated Google, I could use several paid services that offer similar benefits. Snapchat is becoming more popular with the older people I know. Instagram was great before getting bought out by Facebook so we can't count them now.
I think maybe one point that needs to be made, is if you want a "free service" you must be willing to let your data be sold. That is the big problem that many people have with a lot of the above free services.