The MaxSerial is an Arduino Diecimila like board which connects to a regular serial port. Unlike many others, the MaxSerial uses an industry standard MAX232 chip to ensure reliable communication. If you want the USB Diecimila ease of use and reliability but without the USB, this is your best bet.
For maximum compatibility, the kit can be ordered with an optional 3.3V regulated supply, without this, the 3.3V pin is unconnected.
Use the easy to follow assembly directions to build the kit.
This is a full kit containing all of the parts required to build a MaxSerial; you will need to have some soldering ability. You will also need a DB9M-DB9F serial cable or USB-serial adaptor and a 7V to 18V DC power supply/wall-wart.