There's my https://teams.cardsync.xyz/ https://teams.cardsync.xyz/, which I did as toy and forgot about, then months later I realized there were many many users

There's my https://teams.cardsync.xyz/ https://teams.cardsync.xyz/, which I did as toy and forgot about, then months later I realized there were many many users using it for free, then started charging a little and people indeed started to pay! Then many people told me to raise the prices, which I did reluctantly and now I have a nice product that is grossly overpriced, but people pay anyway (not many people, but sufficient to be profitable and perhaps make a very modest living). I recommend first trying out plugins and extensions for established products instead of trying to launch the new Facebook. Stuff like https://www.ragic.com/ https://www.ragic.com/, for example, are niches no one seem to be exploring.