Bluetooth command line tools are a suite of command line utilities for Microsoft Windows that can be used to configure your bluetooth adapter, discover remote bluetooth devices and services, transfer files to OBEX capable devices.
Bluetooth software on CodePlex- http://www.codeplex.com/site/search?query=bluetooth&sortBy=Relevance&tagName=%2cbluetooth%2c&licenses=|&refinedSearch=true
Broadcom offers development kits enabling application developers to write Bluetooth enabled applications for PCs and PDAs. The DK includes application programming interfaces, sample applications, documentation and support.
Portable Bluetooth Stack that runs as a user-space daemon and will support different Bluetooth HCI transport layers. The aim of this project is to support devices for which the OS either does not provide a Bluetooth Stack or the available stack is severely limited (e.g., on the iPhone).
32feet.NET is a shared-source project to make personal area networking technologies such as Bluetooth, Infrared (IrDA) and more, easily accessible from .NET code. Supports desktop, mobile or embedded systems.