Bitcoin (BTC)

The first working system of electronic cash without an intermediary: a network of independent nodes keeps one shared ledger of transfers, and the right to append the next block is won by grinding hashes. That is proof of work, and it rests on a simple calculation — rewriting history costs more than the fraud would earn.

Issuance is fixed in code and capped at 21 million coins. The block reward halves every 210,000 blocks, and difficulty readjusts so that a block is found roughly every ten minutes no matter how much hardware joins. The rules are enforced by no operator but by every node for itself: anyone can run the software, which is precisely why the rules cannot be changed without users agreeing. The spending language is deliberately thin — nodes verify signatures and simple conditions, they do not run arbitrary programs.

Hence the role Bitcoin settled into: a base settlement layer and a long-horizon store of value rather than a venue for applications. Small fast payments and richer logic are bolted on through second layers such as Lightning.

The thin scripting language is a deliberate choice, not an omission: the less the network can execute, the smaller its surface for bugs and for disputes over the rules.