Newton Connection Kit
A consumer product developed by Apple that included the Newton Connection software, a serial cable, and related documentation for connecting Newton devices to Mac OS and Windows computers, allowing the user to exchange and synchronize information with common desktop applications. The Newton Connection Kit is for use with Newton OS 1.x only. The equivalent software package for Newton OS 2.x is Newton Connection Utilities. Also referred to as NCK.
Internet Archive: Newton Connection Kit 1.0 Description
Internet Archive: Newton Connection Kit 2.0 Description
The Newted Community: Newton Connection Kit for Windows User’s Guide (PDF)