1st SPOT APIs

Fast API Search

What is an API?

JavaMath API - Welcome

Python/C API Reference Manual

PEP 249 -- Python Database API Specification v2.0

OPERATING SYSTEM

Microsoft Windows API

The Linux Kernel API

Cygwin API Reference

theForger's Win32 API Tutorial

The GNOME Development Site - API Reference

Linux Audio Developer's Simple Plugin API (LADSPA) Introduction to LADSPA

LWN: API changes in the 2.6 kernel series

Windows API Tutorial

GTK+ - API Documentation

A Java API to read, write and modify Excel spreadsheets

OPEN OFFICE API

Jive Software: Smack API Open source projects at Jive Software

Textamerica Developer API | Textamerica API

Apache API notes

Bloglines | API Documentation

Google Web APIs

Mozilla Plugins API

SAC: Simple API for CSS

Skype Developer Zone

XML-RPC Client/Server Protocol Reference

Zope.org - Appendix B: API Reference