Voyant Tools is an easy-to-use platform for analyzing digital texts. It doesn't require programming skills, and is often a good place to start if you're not sure which form of computational analysis will be best for your project.
VoyantTools can get a word frequency count in your text, as an example.
The Digital Humanities project has produced a Quick Guide to getting started.
The Distant Reader is grant-funded project that provides a tool and platform for analyzing large amounts of digital text (for example, the entire text of a journal). You can provide input text via a plain text file, a URL, or a Zip file.
Example of output from a Distant Reader analysis
You will need to create an account for yourself (it is free) and having some familiarity with a language like Python for web scraping and text processing will let you get the most out of this tool.
Constellate is a project of ITHAKA JSTOR Labs.
This beta project provides a Jupyter Notebooks-based dashboard for performing analyses of the contents of the JSTOR platform, as well as growing numbers of other digitized content contributed by project collaborators.