The Bywater BASIC Interpreter (bwBASIC) implements a large
superset of the ANSI Standard for Minimal BASIC (X3.60-1978)
and a significant subset of the ANSI Standard for Full BASIC
(X3.113-1987) in C. It also offers shell programming facilities
as an extension of BASIC. bwBASIC seeks to be as portable
as possible.

WWW: https://sourceforge.net/projects/bwbasic/