rjmailer is a replacement for the SMTP part of Sun's javamail library. It sends email messages via SMTP and has the ability to connect directly to the receiving mail servers instead of using a relay server, which in many cases can result in more detailed information about the delivery status.
rmachine is a simulator for register machines (in the context of complexity theory), complete with a GUI and a Python module to be used in your programs. The machine ("RAM") is equal to Turing machines in its computional power. It has theoretically unlimited memory (but is limited in practice by your computer's memory).
rmlint is a command line tool to clean your filesystem from various sorts of lint, such as duplicates. It tends to be much faster than fdupes. Additionally, it is able to find empty files and directories, nonstripped binaries, files with the same basenames (nameclusters), old temporary data, strange filenames, and bad links.