Visual Synapse are component wrappers around the Synapse tcp/ip libraries. It wraps a few common internet protocols, like HTTP, UDP, DNS, ICMP, TCP and SMTP to multi-threaded components that can be used with Delphi, Kylix, Freepascal and C++ Builder.
Graficas 2D is an opensource library for plotting 2D functions. It's compatible with .NET Framework and Mono
A set of components and functions for MIDI communication for Delphi. Main development running on BitBucket: http://bitbucket.org/h4ndy/midiio-dev/