Lenovo Thinkcentre/ThinkStation Tiny PCs

The Lenovo Tiny lineup is a series of ultra-small form factor (179mm x 183mm x 34.5mm) desktop PCs that offers near full desktop performance in a highly compact and energy-efficient chassis. Older generations are relatively cheap on the secondary market, and still packs enough compute power for homelab use in a small form factor. 

Those Tiny PCs comes in various models, where often times the lower tier model is a stripe down version of the higher tier model. Through some hardware modding, the lower tier model can be modded and perform like its higher tier counterparts.