In 2016 two early-career researchers met and discussed the lack of open-access materials related to spatial data analysis with vector and raster geo data in R. A few months later, they started writing a book together which, from the first commit onwards, was done in the open. The book source code was publicly available at GitHub, updated regularly, and reproduced on every commit by continuous integration. Due to this approach, it initially attracted several contributors, one of whom became an author. Writing the book using many FOSS tools allowed us to contribute suggestions, leading to dozens of improvements upstream. The first version of Geocomputation with R (abbreviated to 'geocompr') was completed and published in early 2019. 'Geocompr', started as a two-person book project. However, it not only attracted many readers, but also enabled online discussion through online platforms, such as GitHub and social media. In the last few years, the book has had a few hundred thousand readers online, gained a few official and community translations, and has been used in many academic courses and research papers. We also started working on its second edition and its sibling project: Geocomputation with Python. It became clear that the 'geocompr' name was no longer appropriate for the more multilingual nature of the project, and we started using the 'geocompx' name. We hope it captures the essence of the project: eXchanging information about geocomputation, cross (X) pollination of ideas from one programming language to another, and the possibility of hosting additional content on geocomputation with (X) other languages. Currently, the main entry point for this project is the https://geocompx.org website. It contains links to other books and materials and also hosts a blog with posts related to geocomputation, which is also open to guest writers. The 'geocompx' project is also a Discord server with discussions about various FOSS4G topics, from tools and methods to applications to solve real-life problems. In this talk, we will share our experiences of writing an open access book, show the tools we use, and provide suggestions on how to start to contribute or create FOSS4G materials on your own.