Tools for DATA/DICT extraction
These are current tools, through which the contents of a .data file can be extracted with a .dict file.
Toolbox.Reborn (Recommended)
Toolbox.Reborn was created by KillzXGaming and is the most advanced tool for working with .dict and .data files. It can extract textures, models, as well as general data chunks.
GitHub repository: https://github.com/KillzXGaming/Toolbox.Reborn
NLG-File-Editor-Tool (In-development)
NGL-File-Editor-Tool was created by KillzXGaming and is a simple tool to extract/edit files from .dict/data.
GitHub repository: https://github.com/KillzXGaming/NLG-File-Editor-Tool
CTR Studio
CTR Studio was developed by the Map Studio Project, with the primary contributor, again, being KillzXGaming, and is a culmination of previous tools developed for modding applications, like Toolbox.Core and, most importantly for Luigi's Mansion 2 modding, the NextLevelLibrary. The tool allows you to edit files and visualize 3D objects. It is still very much a W.i.P.
GitHub repository: https://github.com/MapStudioProject/CTR-Studio
LM2L
LM2L was created by hadashisora and is presumably the first-ever tool that was able to extract data from Next Level Games' .dict and .data file formats. The tool can extract files from a .data file, as well as the textures contained in it.
GitHub repository: https://github.com/hadashisora/LM2L
Data Extractor and Repacker (In-development)
Data Extractor and Repacker (or D.E.a.R.) was created by Schweini07 as a research project to understand the structures of .dict and .data files. It can currently extract files from a .data file but is planned to be comparable to the ability of CTR Studio.
GitHub repository: https://github.com/Schweini07/LM2-Modding/tree/master/Tools/data_extractor