Recommended Libraries

Databases

Relational

ORMs

Drivers

NoSQL

FFI

C

Java

Scripting Languages

Cryptography

Graphics

GUI

Game Development

Parsing

Data Formats

JSON

(Sabra Crolleton compared the different libraries here)

Data Validation

Network

Email

SSH

IRC

Science

Mathematics

Plotting

Machine Learning

Web Development

Web Frameworks

Modules

Template Engines

JavaScript

Web Service Clients

Web Servers

System Interface

Parallel, Concurrent and Async

Encodings

Localization

Date and Time

Unit Testing

Logging

Language Extensions

Syntax

Type System

Build Systems

Package Management

DSLs

Miscellaneous

Configuration Management

Benchmarking