Free as in beer. I can live without the source code.
About 10 years ago I saw a commercial product. Is there anything free now?
I found Gispf on SourceForge, but there are no downloads. Otherwise, I can't find a thing.
Edit: I'd prefer something approaching the whole system, but could manage to live with the editor
Edit" TSO is "the old Time-Sharing Option on IBM mainframes"
Have tried anything listed on Dave's SPF Editor page