All the Nik plugins can be launched as standalone applications. When launched, some of them display a File menu allowing to open an image file. The plugins can handle TIFF and JPEG files but the filter in the Open file dialog can only be set to JPEG, although selecting TIFF files is possible. This should be fixed.
What’s inconsistent is that DFine, Sharpener and Viveza do not offer a File menu. They have a different interface and were probably written by a different team/author. To run them as a standalone app you have to pass the path of the target file on the command line (which is done automatically when running from DPL, LR or PS). To do this (and many other things), you can use my free ClipName and ExecParm Windows Explorer extensions.
https://www.dropbox.com/s/3kmylgajt6xglpr/Clipname64En.zip?dl=0 (Clipname EN 64-bit)
https://www.dropbox.com/s/1hnxou3sjf96nth/Clipname64Fr.zip?dl=0 (Clipname FR 64-bit)
https://www.dropbox.com/s/rdokyl8ta7mkxb2/ClipNameEn.zip?dl=0 (Clipname EN 32-bit)
https://www.dropbox.com/s/45xeyxjd4vokhx4/ClipNameFr.zip?dl=0 (Clipname FR 32-bit)
https://www.dropbox.com/s/bk2atxmdjjtwfkm/ExecParm64.zip?dl=0 (ExecParm EN 64-bit)
https://www.dropbox.com/s/qodb3p6cx93scmo/ExecParm.zip?dl=0 (ExecParm EN 32-bit)
These extensions are rather old but still working perfectly under Windows 10.
(description and instructions for use are included in the archive)