The Cratylus is a Socratic dialogue notable for Plato's foundational contribution to the philosophy of language.
Free Online and Downloadable Texts
Gutenberg: Cratylus by Plato, translated by Benjamin Jowett, multiple formats.
University of Adelaide (Internet Archive): Cratylus, translated by Benjamin Jowett. EPUB, HTML and MOBI formats.
History of Philosophy without any gaps: What's in a Name? Plato's Cratylus - podcast by philosopher Peter Adamson.
Leiden University Classics Department: A Bibliography on Plato's Cratylus.
Librivox: Cratylus audiobook
PhilPapers: Plato - Cratylus - bibliography with open access option.
The Great Conversation: Further reading at Tom's Learning Notes
Ancient Greek resources: Learn to read Greek classics in the original.
Bloom's Western Canon: Plato's Dialogues are listed.