CHM is a compiled help file format used for delivering help documentation. It stores text, images, and other multimedia elements in a single file. CHM files are commonly used in software applications to provide user guides, manuals, and other technical documentation that can be easily accessed by users.
OEB is an ebook format used by the Open eBook standard for digital publications. It supports rich text, images, and hyperlinks, and is commonly used for distributing digital books and content. OEB files are now considered obsolete, replaced by the more widely used EPUB format.