Cheap Home Automation.
Use an Arduino to control power-sockets in your home.
Step 1: Get a pack of "SMJ remote controlled sockets".
Step 2: Allocate channels (A-D) and buttons (1-3) to lamps and gizmo's around your home.
Step 3: Connect an Arduino to an Aurel Wireless RTX-MID-3V transceiver (see code for mapping).
Step 4: Load sketch on your Arduino (v11 is latest).
Step 5: Place batch file (Windows). Your com port might not be com3.
Step 6: Set up windows task scheduler. Get fancy...