What is Ripple:
Ripple is a blockchain protocol for inter-bank settlements. Ripple is designed to work with existing institutions to facilitate the ability to quickly transact any asset globally. The Ripple protocol’s native currency, XRP, is only required to pay fees for transactions on the Ripple network. It can be used in other instances, but banks have the option to transact IOUs in any asset, including USD, EUR, and other fiat currencies. Ripple Inc. builds an infrastructure protocol that facilitates decentralized exchange of assets between banks.

What are the current challenges:
If our banks do not have a trusted relationship, then we must wait for the money to actually be transferred, or the transaction must be routed through a mutually trusted third party. Both of these processes are slower and more costly than simple IOU issuance. These transfers are more complex across borders, where banks are less likely to have trusted relationships.
Bank in India and bank in China, may not have a trusted relationship. If I want to send money from my account at Bank in India to my friend’s account at China, the payment must route through multiple parties. Each transaction has a cost and takes time. Thus, international payments are slow and expensive.

There are third parties such as Visa, Mastercard, Money Exchange, etc involved would charge high transaction fee and cumbersome settlement process that are executed by different parties to reconcile the single transactions made between the persons.
The transactions go through multiple parties where there are potential possibilities of delay, slow to process, expensive. Each bank has to hold certain amount of liquid with third parties for trust.
How the Ripple solutions:
Ripple allows banks to move from a system of disjointed, trust-based databases to a single distributed database, the Ripple ledger. This gives transactions a fluidity and speed that can’t be achieved in the legacy system, and it greatly frees up working capital. Ripple solves real problems for banks. The Ripple network is essentially a map of trust lines. When two parties wish to exchange value, but do not have a direct line of trust, Ripple routes the transaction through the fastest and shortest possible path of trusted parties, enabling global parties to transact instantly without establishing new trust lines. The network provides a distributed ledger that logs all of these transactions.

Ripple Network as a Trust Map:
Imagine the Ripple network like a giant map where each connection between people or banks is a "trust line." If you want to send money to someone but you don't directly trust them, Ripple finds the shortest and quickest route through other trusted connections to move that money.
How Transactions Work:
No Direct Trust? No Problem: If you (let's say, User A) want to send money to someone (User B) who banks with a different institution, you don't need to open an account with their bank. Instead, your bank (BankX) issues an IOU (I Owe You) on the Ripple network in XRP, or it can be any fiat or crypto currency, for example, RLUSD.Different Banks, Different IOUs: Even though both BankX and BankY issue USD IOUs (RLUSD and USDT), they might not be exactly equal because the risk of one bank failing could make one IOU more valuable than the other.Sending Money: If User A wants to send $50 to User B:BankX issues $50 worth of RLUSD on the Ripple network.This IOU travels through the network to find the best path to reach User B, who might use BankY.Conversion:The transaction goes through an "order book" where someone (a market maker) who holds both types of USD IOUs can convert RLUSD to USDT.This market maker might make a small profit because BankX-USD could be worth a bit more than BankY-USD due to differing trust levels in the banks.Completion: Once converted, $50 in BankY-USD reaches User B's account at BankY.

What is RPCA?
Ripple Protocol Consensus Algorithm (RPCA) is like a voting system for a group of computers (called nodes or servers) that all want to agree on the same information or "truth" about transactions in the Ripple network.
How Does It Work?
Unique Node List (UNL):Each server in the Ripple network has its own list of trusted friends, known as a Unique Node List (UNL). A server only listens to these friends for updates on transactions.Transaction Proposals:Servers suggest groups of transactions (like a grocery shopping list) called "candidate sets." These are proposals on what should be recorded in the shared ledger (the official record of all transactions).Consensus Process:Servers keep swapping these lists back and forth until 80% of the servers in their UNL agree on exactly which transactions should go into the ledger, in what order.Reaching Agreement:If 80% agree, those transactions get added to the ledger. However, for the entire network to agree, there needs to be enough overlap between different UNLs.Network-Wide Consensus:If there's not enough shared trust (at least 40% overlap between UNLs), different parts of the network might agree on different things, which could lead to a "fork" where there's no single agreed-upon ledger.
In Simple Terms:
Imagine you and your friends are deciding what to eat for dinner. Each of you trusts a few friends to suggest dishes. You keep discussing until most of your trusted friends agree on a menu. But if your group of friends doesn't overlap enough with another group, you might end up with two different dinner plans. Ripple works to avoid this by ensuring there's enough common ground among all groups to agree on one dinner menu (ledger) for everyone.

Ripple Market Capital as of Dec-2024:

Nodes of decentralized Ripple:

Status nodes and validateors updated to recent version:

Source: https://assets.ctfassets.net/qtbqvna1l0yq/61a7RTBGW3oqE8gfj20mtZ/840adacd9ce65622d693623d9d6d40fa/Ripple_Analysis.pdf