An engineer is simply an individual that can do for a dime what any fool can do for a dollar.
I thought this would be a mental exercise back in 2004, but it ended up being the lynchpin for two professional projects in 2012: one with Valparaiso University's Solar Research Facility and another with a local company, Sundolier.
My second project on Hackaday, a portable bench supply with over 10Ah of Li-Po, protection circuits and an on-board charger. Limited to 12V@500mA, it was nonetheless very helpful for low power shop floor projects that ran for long periods.
My first DIY bench supply; +/- 0-24V @ 1.5A, Fixed 5V@12A and 3.3V@5A. Built out of surplus parts and a beefy transformer out of an old projection TV.
My first project on Hackaday, reusing an old laptop as a second monitor. In mid-2007 using just the LCD would have been an expensive proposition: LVDS cards were $200-$500, so I piped it over a network connection.
Circa 2007, my first ground-up CNC build. Runs EMC2 (now LinuxCNC) with spindle control, M-Code vacuum and a custom pendant.