Texas Instruments TI Programmable 57
The TI-57 was a programmable calculator made by Texas Instruments from 1977 to 1982, which was followed by the more powerful TI-58 and TI-59. It had 50 program steps and 8 memory registers.
I owned a Texas Instruments TI-57 while at university, used very occasionally for 'real' problems but mainly just played with the examples provided and created my own games. While Moon Lander on an 8 character mono LED display wasn't tremendously exciting, it was a great exercise in compact programming. I have yet to try and recreate this.
My current one was bought on eBay and worked with the power supply attached but the rechargeable batteries, not surprisingly, didn't charge. I attempted to repalce them with new rechargeables but couldn't get that to work so eneded up squeezing a 9v PP3 into the battery compartment instead. More on that later.