If you want to play with BASIC on a modern computer, here are two options I have found.
PC-BASIC

PC-BASIC is an implementation of the old GW-BASIC that came with MS-DOS. It allows you to enter commands directly (PRINT “HELLO WORLD”) just like the old days, and also write full programs with line numbers. You can load and save them just like you’d expect. This one should be familiar to those who have used Microsoft BASIC on other systems.
http://robhagemans.github.io/pcbasic/
I found PC-BASIC awhile ago when I was working on my SirSound project. I was trying to find out how Microsoft supported multi-voice music on their BASICs that supported it. I have since used it for various quick-and-dirty experiments, even in my day job (most recently, to draw out a user interface for an embedded device I am working on).
QB64

Special thanks to Art Flexser for letting me know about this one.
This is an implementation of QuickBasic from the MS-DOS days. It allows writing a more modern version of BASIC, and compiling it down to an executable.
I have not used QB64 yet, beyond making a simple “Hello World” program, but it looks promising.
If you know of any other cross-platform BASICs (Windows, Mac and Linux) I should try, please mention them in the comments. Thanks!
Until next time…
Have you considered? It’s almost like the Basic language answer to freepascal and is multi-platform.
https://www.freebasic.net/
Thanks for the tip! I’ll check it out and add it to the list, along with Microsoft Small BASIC which was also suggested. Who knew that BASIC was still alive and well.