The Raspberry Pi can be used to connect vintage computers to the internet. This image shows my preference - A USB wireless dongle and a USB to serial cable. One could also use the serial port of the Pi, but that method is not covered here.
The operating system I chose is a version of Debian Linux tailored for Apple II use (search the web for "IvanX" to download a copy with directions), but this Pi distro is also good for most other terminal software-driven vintage computers. Click for larger view.

Pictured is the rear of a Commodore CBM 256-80 computer. Note the use of the null modem adapter, this is required to connect to the Raspberry Pi as a terminal. The serial to USB cable connects to one of the two USB ports of the Pi. Click for larger view.

The rear of an Apple /// computer and the necessary RS232 serial port connection. Click for larger view.

You will need a terminal program that is compatible with the version of Linux you're running on the Raspberry Pi. BeeLine For the B series CBM line provides enough options to allow a connection with minimal garbled characters. It's not easy and a lot of little Linux-y tweaks and experimenting will be necessary to get things just right. I already configured inittab to open ttyUSB0, but I had to noodle with the baud rate and terminal type. See /etc/inittab. I ended up settling on 1200b 7/1/E/N. Click for larger view.

Here is a good example of what to expect when you boot. At first, while the system initializes, you may see garbled characters, this is normal. Eventually however you should expect a login prompt. Click for larger view.

Here is the Apple III after successful connection. Click for larger view.

Apple /// connection, not quite right...more adjustments are needed. I eventually settled on a program called MicroTerminal for the III. Pictured is a screen shot from EasyTerm. Click for larger view.

This is the Commodore using the email program mutt to pull email from my gmail.com account. Click for larger view.