Here are my ZX Spectrum Next utility applications.
These applications are for Microsoft Windows.
Image To Layer 2
An application to convert a bitmap to raw bytes and also extract a 9-bit colour palette. 
Bank Pack
An application to generate bank files and include files from a collection of smaller asset files.
Nex Builder
A command line tool to build NEX files, with a built-in GUI command line generator.
The applications are open source and are released under the MIT Licence.
Next Utilities R2
Included in the installer are the binaries and the C# source code.