I was browsing Amazon one day and came across a super tiny, super cheap mATX case that I thought would be fun to build in. This one is a mix of new and used parts from Facebook Marketplace. I put the can of Coke in the photo for scale, and the velcro handle makes this one's small size extremely portable.
Jonsbo C6 mATX Case
Asus TUF Gaming A520M-PLUS
Ryzen 5 3600x
Thermalright AXP90 Low Profile CPU Cooler
MSI RTX2070 Super
16GB DDR4 3200 Ram
1 TB Crucial P3+ NVME Drive
Corsair CX650M PSU