SDF (Super Dimension Fortress) is such an amazing discovery that I just can't seem to put into words how excited I am about it. Is it a bit geekish? Very likely, that's why I love it even more. I became an ARPA member from the very beginning. After a 30 day period I can become a MetaARPA.
I wanted to make a list of the most outstanding things that you can find at sdf. However the list is so huge that I do not think I have the energy to do so. That's why I have taken the easy way out which is linking to sdf's own recommended starter links:
Anyway, let me list some of the features (only a few) that I have tried so far:
shell selection, ssh, telnet, irc, im, mail, games, gopher, web browsing, text editting, file transfer (ftp, scp), compiling...