GNU parallel is a shell tool for executing jobs in parallel locally or using remote computers. A job is typically a single command or a small script that has to be run for each of the lines in the input. The typical input is a list of files, a list of hosts, a list of users, a list of URLs, or a list of tables. If you use xargs today you will find GNU parallel very easy to use, as GNU parallel is written to have the same options as xargs. If you write loops in shell, you will find GNU parallel may be able to replace most of the loops and make them run faster by running several jobs in parallel. GNU parallel makes sure output from the commands is the same output as you would get had you run the commands sequentially. This makes it possible to use output from GNU parallel as input for other programs.
SyWiCo is a tool for managing concurrent modifications of shared files between unconnected computers. It can be used as a synchronization tool relying on email. Its main design goal was for synchronizing the source code by email between developers, when the use of a source control software is not possible. The communication is stateless and reduced to a very small number of messages, typically 2 or 4. It does not create any files in the directories that it synchronizes, and leaves one participant free from dealing with merging and conflict resolution. This is not a tool to replace source control programs, as it provides no versioning.
Boolean Expression Solver is a commandline utility that generates a truth table for a given Boolean expression. It is written in Java, so it will run on any platform that has the Java runtime environment installed, but the makefile and shell-script included for convenience generally require *nix.