Builtin modules

Built-in modules are already installed with Node.js, so you don't need to install them with any package manager (yarn, npm, etc.).

fs: dealing with the system files.
os: provides information about the operation system.
net: to build clients and servers.
path: to handle file paths.
url: help in parsing URL strings.
events: provides a method for interacting with events.
http: making Node.js transfer data over HTTP.
console: to log information in the console.
assert: provides a set of assertion tests.
process: provides information about, and control over, the current process.
cluster: able to creating child processes that runs simultaneously and share the same server port.
perf_hooks: provides APIs for performance measurement
crypto: to handle OpenSSL cryptographic functions.
Buffer: provides APIs to handling streams of binary data.
DNS: enables name resolution.
events: for handling existing events and creating custon events.
child_processes: provides the ability to spawn subprocesses.
REPL: provides a Read-Eval-Print-Loop (REPL) implementation that is available both as a standalone program or includible in other applications.
readline: provides an interface for reading data from a Readable stream one line at a time.
util: supports the needs of Node.js internal APIs.
querystring: provides utilities for parsing and formatting URL query strings.
string_decoder: provides an API for decoding Buffer objects into strings.
tls: provides an implementation of the Transport Layer Security (TLS) and Secure Socket Layer (SSL) protocols.

Free Content API documentation of Built-in modules Built-in modules - w3schools