JSTransform is a utility for transforming JavaScript syntax using the esprima parser, allowing developers to write and apply custom syntax transformations or use pre-bundled ES6/ES7 transforms. It supports multiple transformations in a single pass, source map generation, and offers both an advanced API for fine-grained control and a simple API for automatic transform selection. The project is deprecated in favor of Babel or Recast, but still maintained for existing use cases.