Alchemy is a Blockchain developer platform with a variety of different products to streamline the whole dApp lifecycle. From local development to running it in production.
Their <a href="https://www.alchemy.com/supernode">Supernode API</a> offering provides developers reliable access to the Ethereum Blockchain Network. Other solutions revolve around notifications as well as remote monitoring and debugging.
While paid plans are an option they also offer a generous free plan which should be more than enough to get you started.

Alchemy

Participating in the Ethereum Blockchain Network requires a connection to an Ethereum Node. With Infura you can get API access to a Node without running one yourself.
Their generous free plan should be more than enough to get you started with your Smart Contract and dApp projects. Once outgrown, upgrading to the next tier is a matter of a few clicks.
Protip: Infura allows you to connect to their network via WebSockets (<code>wss://</code>) which can help you save bandwidth and API credits with read- and write heavy operations.

Hosted RPC Nodes for Ethereum Virtual Machine (EVM) based Blockchains.

Optimism

Alchemy

Infura