Sidekick

SideKick was an early Personal Information Manager (PIM) software application by Borland. It was notable for being a Terminate and Stay Resident (TSR) program, which enabled it to load into memory then return the computer to the DOS command prompt, allowing the user to load another application program, but still activate SideKick using a hot key combination (by default: Ctrl-Alt).

Related: T-Mobile Sidekick, T Mobile Sidekick Skin