The OIScript extension library is a simple library that allows you to open and interact with dialog boxes created through Neuron Data's product. It is not an extension like Spatial Analyst or Network Analyst. It has been part of the ArcView since version 2.0.
When you buy Neuron Data's OpenInterface software, you get its OpenEditor. With OpenEditor, you can create modal or modeless dialog boxes. You can use OIScript to open these dialog boxes from Avenue.
The library that supports this functionality is part of ArcView and is delivered in the arcview\bin directory. If you are on UNIX, it is liboiscript, and on PC or Mac, it is oiscript.dll. You must load this library using the System.LoadLibrary command. You can then use the Window class (modeless dialog boxes) or ModalDialog class to open these dialog boxes from Avenue.
While the OIScript is available, it is not a solution we strongly advocate (hence the limited documentation). If ArcView ever moves from Neuron Data, this functionality will no longer be available. Additionally, although ESRI will not be deleting OIScript from ArcView for current customers, there will be no further development on it and no additional documentation. We very much encourage the use of dialog boxes (see the Dialog Designer Extension).