I bought an old 4th-gen i5 Dell Optiplex on eBay for like $200, cleaned & repasted it, loaded 16GB of RAM into it, a DVD-burner, an old SSD for the boot drive, and gave it to my mother-in-law to use. It works beautifully for her. It was a great deal. I took my old Dell Inspiron 13 7359 (i7-6500u) and installed Chrome OS on it and gave it to my son. Chrome OS works amazingly on it compared to any version of Windows. My old XPS 410 is still running since 2006. I took out the Core2 Duo 6400 (one of the first dual-core), and bought a Core2-Quad QX-6800 CPU ($1600+ when it was new) for $50, installed an SSD, expanded the RAM beyond spec to 8GB, and installed Windows 10 on it. It still works for basic office-type stuff, but that thing is seriously 16 years old and works reliably well for a non-profit I work with. Sadly, I just recycled the monitor last week, a Dell UltraSharp 2007WFP.  
Other than recycling, what are some ways you have repurposed an old system? For more questions regarding this contest, please visit the Information Page here.
DS 07/25: Other than recycling, what are some ways you have repurposed an old 
system?