Welcome to the world of BC BASIC programming. This package will enable you to get the most from your Commodore 64, whether you are a computing expert or just a beginner. BC BASIC makes the 64's advanced facilities, such as hi-res graphics, sprites and sound, easy and simple to use by means of many fast and powerful commands and functions added to the BASIC language. Whatever you use your 64 for, from writing games to serious applications, BC BASIC will help you do it much more easily and quickly.

NOTE - here is a link to the manual.

Here's a link to an interesting comparison between Simon's BASIC and BC BASIC.