DOSbox works to run gwbasic and many older dos programs.
To install it: sudo apt-get install dosbox
To run it: dosbox gwbasic.exe
Caveats: DOSbox emulates a processor, so it runs applications slower than on Wine or as a native application. However, everything that originally ran on 486 should work fine with DOSbox.
Speaking of gwbasic, by default it saves the source code in binary format. You can save the a (ascii) switch in text format, for example:
save "filename",a
As for the base interpreter that runs gwbasic code on Ubuntu, I haven't found it yet, but I'm still looking.
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