FreeBASIC
FreeBASIC is a 32/64-bit, cross-platform, Microsoft QuickBasic compatible, modern object-orientated language in the BASIC family and has headers for numerous add-on libraries. It has official ports for Windows, Linux, and other modern Unices including FreeBSD, OpenBSD, etc, and 32-bit DOS. We use a fork of FB with more complete support for Mac OS and Android.
Think of FB as a subset of C++ with BASIC syntax and some additions & improvements -- FB has equivalents of nearly all features of C++98 except templates. It even has a significantly better-designed reimplementation of the C preprocessor, and easy to use strings.
The OHRRPGCE was originally written in QuickBasic (QB) but it has been ported to FreeBASIC.
FreeBASIC has four different dialects, including "qb" which has very high compatibility with QuickBasic. We use the default "fb" dialect, which is the most C++-like dialect and removes a lot of QB syntax like GOSUB.