In one of the most unique DIY projects, Reddit user PickentCode has created what can be described as a completely off-the-grid "heat engine computing device." Originally patented in 1816 by the Scottish minister and inventor Robert Stirling, a Stirling engine converts heat directly into mechanical energy. "The entire project took about a month to design, build, and program," PickentCode told Tom's Hardware. The model Stirling engine can produce only 150 milliwatts of power, and to stay within this tiny power budget, the creator implemented certain hardware and software optimizations. Stay On the Cutting Edge: Get the Tom's Hardware Newsletter Get Tom's Hardware's best news and in-depth reviews, straight to your inbox.