Python for Delphi (P4D) is a set of free components that wrap up the Python DLL into Delphi. They let you easily execute Python scripts, create new Python modules and new Python types. You can create Python extensions as DLLs and much more.

Simple DirectMedia Layer is a cross-platform development library designed to provide low level access to audio, keyboard, mouse, joystick, and graphics hardware via OpenGL and Direct3D. It is used by video playback software, emulators, and popular games including Valve's award winning catalog and many Humble Bundle games.

Google's C++ test framework.

IPWorks is a comprehensive framework of easy-to-use components for Internet development, including FTP, HTTP, SMTP, POP, IMAP, LDAP, DNS, SMS, SOAP, etc.

Xerces C++ is a validating XML parser written in a portable subset of C++. Xerces makes it easy to give your application the ability to read and write XML data. A shared library is provided for parsing, generating, manipulating, and validating XML documents.

TinyXML-2 is a simple, small, efficient, C++ XML parser that can be easily integrated into other programs.

This is Expat, a C library for parsing XML, started by James Clark in 1997. Expat is a stream-oriented XML parser. This means that you register handlers with the parser before starting the parse. These handlers are called when the parser discovers the associated structures in the document being parsed. A start tag is an example of the kind of structures for which you may register handlers.

nrComm Lib provides tools for performing the serial communications tasks and device access. It has ready solutions for: serial rs232 lpt ports, usb, bluetooth, hid, modbus, gsm, sms and others.

TsiLang Components Suite includes a number of highly professional, easy-to-use VCL components, wizards and tools for building multi-language and localized applications under RAD Studio, Delphi and C++Builder for Windows, Android, iOS and OSX platforms.

GLibWMI is a Delphi library of components, focused on the Administration of Windows Systems. They are based on Windows WMI (Windows Management Instrumentation).