API Wrappers

In addition to the default way of accessing Trillian in plugins via C, there are wrappers for other languages.

The Dent Project is an open source API for writing Trillian plugins in C#, Visual Basic .NET, or Managed C++. It is currently in its initial stages of development. For more information on this project, visit the Dent Project homepage.
A Delphi-plugin.pas, according to the C-plugin.h, is available for download from here. See Your First Delphi Plugin for an introduction to the topic of developing plugins with Delphi.
Wiki documentation for the Delphi wrapper library.
Tcllian is a Trillian plugin that provides Tcl bindings to many of Trillian's plugin API functions and callbacks. It's still very experimental, but does work.