Here are the basics:
1. non-custodial and #d14n exchange
2. multi-sig
3. smart contracts
Abra is a non-custodial decentralized exchange. That means they don't own your private keys or hold your coins. When you log into the app, they give you seedkeys which you MUST write down. This is the first half of the 2-2 multisig.
Abra is the 2nd partner. When you deposit LTC and trade for a coin, you sign your 1/2 of the tx to Abra. Your LTC is now locked. When you cash out, they sign their half of the tx and send back to you your gains/losses. Abra covers the spread.
abra.com/blog/crypto-fi…
Here's the slightly confusing part. Abra has made it possible to trade without actually owning many of the coins on their platform. If you buy VTC or ETH, they don't actually own that. They call this a "synthetic currency" that only exists in their platform
The synthetic currency follows the price of the respective coin on exchanges. So the VTC synthetic currency will follow the price of VTC on exchanges. If VTC goes up in value, you can cash out and they will pay you out in LTC.
abra.com/blog/abra-laun…
They've created synthetic currencies for various fiats as well. This is the most interesting part for me because it rightfully leverages gov't and global economies in a similar way derivative markets do.
abra.com/blog/abra-laun…