https://www.gnu.org/software/mit-scheme/release.html
I will try to run SchemeBBS on it soon.
Support for Unicode:
* NFC and NFD normalization is supported; most strings are NFC.
* Conversions between strings and UTF-{8,16,32} bytevectors are supported.
* Symbols, the reader, the printer, and textual ports all support Unicode.
* Character sets now support Unicode, and have been significantly tuned for space, using an inversion list.
* New regsexp regular-expression matcher supports Unicode.