The official repository is at libntl.org , where you can find the latest Unix ( .tar.gz ) and Windows ( .zip ) distributions.
The .ntl file suffix is often related to scripts for the D2NT mod in Diablo 2. Where to Download Download NTL rar
Always use official sources to ensure your downloads are secure: The official repository is at libntl
For other NTL-related projects, reputable hosting sites like SourceForge are common. How to Open a .rar File The official repository is at libntl.org