Dont get rid of that serial plotter just yet!! With RulesPlot it will still work on OSX via USB to serial converter and RulesPlot.

Basics:
RulesPlot is designed to send HPGL data files to a serial device such as a plotter or sample cutter. CAD file output in HPGL or DMP formats (or other formats can be entered) can be sent to a directory on your computer that RulesPlot watches. Once RulesPlot detects a file, it can either be set to automatically send the file to the machine as a "transparent send" or can be listed in the program so that files can be viewed and sent at the user's discretion.

Communications:
An established serial port connection to the plotting device:
Mac OSX must use a USB to Serial adapters (currently shipping version) USB to Serial cable adapters. Refer to the manufacturers drivers for installing and configuring the adapter. USB to Serial adapter usage is optional for Win users provided they have a Serial port and proper cable for the device. The USB to Serial adapter & Mac OSX driver version has been fully tested on Mac OSX and WinXP.

Features:
Automatically sends .hpg or .dmp files that show up in a user defined folder to the device
Allows full serial communication options; data rate, stop bits, handshaking etc.
Optionally can scan a folder selected by the user and queue files to send one at a time
Displays the file contents for preview in the plotting queue
Runs both modes simultaneously