XC=BASIC supports third-party extensions since version 2.2. Extensions are includable source files that define

• new COMMANDS
• new FUNCTIONS
• new CONSTANTS
• new VARIABLES

Extensions can be written in assembly language or in XC=BASIC as well if speed is not crucial.

• xcb-ext-sprite - commands for all sprite operations and functions for polling collisions
• xcb-ext-hires - commands for hi-res drawing
• xcb-ext-joystick - functions for polling joystick states
• xcb-ext-rasterinterrupt - raster interrupts
• xcb-ext-sfx - routines to play S.E.U.C.K sound effects
• xcb-ext-io - extension that handles I/O routines

Just use the INCLUDE directive to include the extension into your program:

include "path/to/extension.bas"

After this point you can use all the new symbols that the extension defines.

Please refer to this tutorial.

Here are some extensions that would be cool to have:

• Music and sound FX commands
• Commands to play SID tunes
• Multicolor drawing
• Library for fast character graphics and scrolling
• Number formatting, i. e. converting numbers of different types to strings in decimal, hex, etc
• Packing/crunching
• Math functions