Scheme+ for DrRacket by Damien Mattei.
The documentation is here: https://github.com/damien-mattei/Scheme-PLUS-for-Racket/blob/gh-pages/README.md
With Racket you do not need to define/declare a variable with the Scheme+ operator <+. Because the binding of the variable is autodetect you can simply set the variable with <- (or :=) and Scheme+ will do the job.
The Racket GUI can not display the line of error in a Scheme+ program. If you have to debug your source code you must generate a Scheme file from your Scheme+ file with curly-infix2prefix4racket and load the result file in Racket GUI. Then you will have all the debug information of Racket on the scheme file.
What's next? i'm working on a cleaner version internally that will use better the scheme macro systeme, that will rely more on macro than on the parser. That will be faster due to more work at expansion stage of the macro using syntax transformers and less job in evaluation stage at run-time. Also i will allow an additionnal syntax (only for Racket) asked by an user.