audio/libsidplay 1.36.60_1 MidnightBSD

Basically, SIDPLAY is just an ordinary music player software. More specifically, it emulates the Sound Interface Device chip (MOS 6581, known as SID) and the Micro Processor Unit (MOS 6510) of the Commodore 64 on your computer. Its platform-independent software emulates hardware components. Therefore it is able to load and execute C64 machine code programs which produce music or sound. In general, these are independent fragments of code and data which have been ripped from games and demonstration programs and were transferred directly from the C64. All you need is a supported operating system and audio hardware with average PCM waveform playback capabilities. A fast CPU and a 16-bit sound card are recommended for better performance.

This is just the library. To actually use it, you need one of the front-ends like 'sidplay' or 'xsidplay'.