Here you can download web-based applications I've created by myself.
If you are studying for CompTIA A+, Network+, or Cisco CCNA, you need to know how to do subnetting. An HTML file is self-contained, so you can run it locally in your web browser.
This is a PHP-based web application for writing notes in HTML and viewing notes in your web browser. It's lightweight and only requires Apache and PHP (recommend PHP 7.0 or later). No MySQL or MariaDB database is required. This is great if you have a virtual machine such as VirtualBox, KVM, Xen, or VMWare. Plus, it's cross-platform.
Here is a license for GNU Affero General Public License v3.0. I chose the license as I think it's made for web applications, even for web applications that can be used internally, such as in virtual machines. Please do release the source code if you modified the web application so that I (and others) can make use of the source code.