Yabasic implements the most common and simple elements of the basic language. It comes with goto/gosub, with various loops, with user defined subroutines and libraries. Yabasic does simple graphics and printing. Yabasic runs under Unix and Windows, it is small, open source and free.
To learn more about yabasic, you may view the Manual of yabasic, browse the faq or read its history or the log of changes and bugs.
This is a simple hello-world.yab written in yabasic, complete with the resulting screenshot:
clear screen print "Press 'q' to quit ..." label again print color("green") "Hello "; print color("blue") "World ! "; if (inkey$(1)="q") exit goto again