SDF is a public access UNIX system. The site has many tutorials about how the SDF UNIX system, some of them are an introduction to this system, how to find help, transferring files, instant messaging, file permissions and many more.
If you want to support this site, you can do so in the form of donations or buying merchandise such as pins or t-shirts. There’s a forum where you can register and talk about a wide variety of topics such as gaming, projects, utilities and technical problems among other things. The page also has a site map so you get what you are looking for without wasting any time. The page also features an FAQ’s section that thoroughly explains topics such as chat, email, hacking and internet connections. 
