The Nik Tools provide a lot of image editing / enhancement options for photos and presentation images. When it was a standalone company, the suite of tools was a good value at $500. After Google bought Nik, it was a great value at $150. Effective today, Google is making the collection of tools free to everyone!
But if I understand correctly you can use these tools only if you are using a compatible host application, like Photoshop, Lightroom, Aperture or Photoshop Elements, since these are essentially plug-ins:
They can all be used stand-alone - but carefully. In stand-alone mode, there is no File menu for Open or Save As. So, a copy of your image should be made first for safety. Then, right-click the image and Open With > [Nik tool] - adjust as desired and click Save, replacing the image file.
Hosting is best (layers). But standalone is fine for folks on a budget (students).
I found this blog that gives some more details for people without Photoshop, Lightroom, etc: