Welcome here,
Well we are doing everything “from scratch”. We do not use any external API or anything else 
There are many reasons to it, that I will not describe here.
You should try Duniter software and join our Testnet currency to take a look at the current state of affairs. Also, you could read past talks we had on the forum.
Generally, we are speaking a bit too much french and it’s not easy for world wide people to join us, so do not hesitate to ask questions We are available on xmpp too, almost 24/24.