basE91 is an advanced method for encoding binary data as ASCII characters. It is similar to UUencode or base64, but is more efficient. The overhead produced by basE91 depends on the input data. It amounts at most to 23% (versus 33% for base64) and can range down to 14%, which typically occurs on 0-byte blocks. This makes basE91 very useful for transferring larger files over binary insecure connections like e-mail or terminal lines.
retty is a utlity that can attach to processes running on another terminal. This is useful, for example, when you run an application locally and then decide you want to use that running application from some remote location. You can run retty on it, do your work, and detach application back again. Its advantage over screen is that you don't have to run the processes on retty in advance.