There are a few ways to host a single HTML file for free:

1. GitHub Pages: GitHub Pages allows users to host static websites for free, and it supports custom domains. You can create a new repository, upload your HTML file, and GitHub will automatically serve it as a website.
2. Google Drive: Google Drive allows users to host a website by creating a new folder, setting it as “public on the web,” and then uploading the website files to that folder. You can upload your HTML file, get the shareable link and use it as a website link.
3. GitLab Pages: GitLab Pages is similar to GitHub Pages, it allows you to host your static websites for free, and it also supports custom domains.
4. Firebase Hosting: Firebase Hosting is a web and mobile app development platform that allows you to host your web applications for free. You can create a new project, upload your HTML file, and Firebase will automatically serve it as a website.
5. Amazon S3: Amazon S3 is a object storage service which allows you to store and retrieve data. You can use the S3 service to host your html file.
6. Neocities: Neocities is a social platform for web developers that allows you to host your HTML files for free.

Please note that while these services are free, they may have limitations on features, performance, and customization. Additionally, some of them may have limitations on number of visitors, uptime guarantee, and support.