selector is a command line utility for dynamic string selection. It reads the content of the specified files, and as the user types a list of strings separated by ";" (or a regexp), the display is updated in real time to show only the lines containing all the said strings (or matching the regexp). This command was mainly designed as a way to search in the shell history, for which it is substantially more efficient than the standard readline ^R binding. With the -v option, it injects the selected line into the tty input buffer, hence allowing the user to edit the line and execute it as a standard command.
pulseaudio-mixer-cli is an interactive ncurses UI to control the volume of PulseAudio streams. It is somewhat like alsamixer, but focused not on sink volume levels (which can actually be controlled via alsamixer, with the alsa-pulse plugin), but rather on the volume of individual streams from applications, allowing the user to balance sound levels between them. Interaction with pulseaudio is done through the DBus interface, and the UI is designed to be as simple as possible, without heavy DE dependencies like GNOME libs or KDE/QT.