The BrewStir. It's a magnetic stir plate for homebrew.

thingiverse

I've upgraded the design of my magnetic stir plate by integrating a speed-controlling regulator directly into the system, utilizing a reliable 12VDC fan. Key improvements have been incorporated in Version 2.\nThe updated design now features adjustable feet made possible by incorporating #8 screws, which allow for more stability on any surface.\nTo witness its capabilities firsthand, view this early test video: https://youtu.be/LTQn-agubDQ\nIn the unconnected component you'll see at the start of the short video, a voltage regulator is shown. Later it's incorporated as an effective speed controller to enhance performance.\nGive my homemade stir bar a try if you like; keep in mind that genuine ones yield far superior results and can be acquired affordably. Instructions for Assembly Recent Improvements The in-line explanation of the improvements made has been updated. An 80mm x 20mm fan running on DC voltage of 12 volts is utilized in this magnetic stirrer system. There's sufficient space created within the housing to accommodate a particular DC-to-DC converter with matching screw holes and an optional potentiometer layout as seen in this item. I took advantage of my designed specifications, opting for .3mm layer settings on the print (using two full layers for 100% filling). Even though my screw threads didn't require extra pressure to install due to precise dimensions, additional stability is offered by using small machine nuts under each set-up. A stable hold was secured on both sides using five strong flat-head #2 screws of 3/8 inch in length for securing the electronics section of the stir plate firmly in its designed place.