There are several platforms through which you can publish OER textbooks.
Pressbooks is the platform being used by the CAUL Open Educational Resources Collective and other Australian university OER publishers (e.g. Western Open Texts from Western Sydney University and RMIT University Open Press). Pressbooks is an online book content management system that allows authors to design and publish online books in a variety of formats. They provide a number of pre-formatted book templates which make the authoring and creation experience easier. Use the links below for access and support for Pressbooks:
This platform allows you to share documentation and other resources you create with selected users, or with everyone. Create pages and organise them into collections to share with collaborators, including students.
MERLOT (Multimedia Education Resource for Learning and Online Teaching) provides access to curated online learning and support materials and content creation tools. Create or adapt material to include in or support your OER textbook.