Static site generators allow developers to make a web site that has many properties of dynamic web sites, except it generates static HTML which can then be uploaded to Neocities.
Hugo
Jekyll
Next.js
Gatsby

Currently Allowed File Types

Neocities is best with files that are used for making static HTML web sites, such as:

HTML (.html, .htm)
Image (.jpg, .png, .gif, .svg, .ico)
Markdown (.md, .markdown)
JavaScript (.js, .json, .geojson)
CSS (.css)
Text (.txt, .text, .csv, .tsv)
XML (.xml)
Web Fonts (.eot, .ttf, .woff, .woff2, .svg)

This is not a complete list of the file types we support, but it is still recommended that you focus on files used for making web sites. The full list of supported file extensions is:

asc atom bin css csv dae eot epub geojson gif gltf htm html ico jpeg jpg js json key kml knowl less manifest markdown md mf mid midi mtl obj opml otf pdf pgp png rdf rss sass scss svg text tsv ttf txt webapp webmanifest webp woff woff2 xcf xml

In addition, we have measures in place to prevent hotlinking of content from non-Neocities sites.
Why are there restricted file types?

At the moment, Neocities is trying to grow sustainably. Our goal is to provide you with a free web site so you can arrange content in any way you want. In order to make sure we can continue to do this, we need to put in place measures to prevent Neocities from becoming a "file dump host". We don't currently have the resources to deal with preventing this from happening if we let users upload anything they want, so the temporary solution for now is to only allow file types that we know are useful for making web sites.

For example, allowing users to host executable (EXE) files provides a way for attackers to host malicious content, and we want to minimize that. Also, if the site starts being used to host malicious content, it is possible that search engines like Google will punish us in rankings, or that our datacenter operators would tell us we can't do business with them, which would affect everyone's site on Neocities.

MP3 music and MP4 video has similar problems, because if the uploaded content became very popular ("goes viral"), it would overwhelm our servers and make our bandwidth much more costly. And hosting rich-media content directly is almost never the best way to do it. Soundcloud provides a great way to host music, and Youtube does a very good job with taking your video, processing it, making sure it works on all browsers, and then provides an easy way for you to embed that content in your web page.

If you have a file type you believe should be allowed, please contact us and we will see if we can put it in for you.

We are constantly working on upgrading our infrastructure to deal with these problems more effectively. Until then, we have a whitelist of allowed file types, but we will let you know if this changes in the future. Thank you for your understanding.
Is there a way to remove the whitelist?

Yes! If you become a supporter, we will remove the whitelist for your file uploads, and you can upload anything you want (except illegal/copyrighted content, of course)! Becoming a supporter reduces the "file dump" risk, which makes it a lot safer for us to allow file uploads of any kind.

Keep in mind that it's still better to host things like videos on Youtube. They've spent a lot of time and invested a lot of money into building a platform for sharing high-bandwidth video very efficiently all over the world. And they don't charge you for bandwith, even if your video becomes very popular (infact, you can make money by sharing their advertising revenue with them).