OS X Snow Leopard (10.6.6) up to High Sierra (10.13.x) works with a Sandy Bridge system
OS S Mountain Lion (10.8.2) up to macOS Catalina (10.15.x) works with Ivy Bridge system.
OS X Mountain Lion (10.8.4) up to macOS Monterey (12.x) works with Haswell systems, depending on the SMBIOS used.
For an old version of OS X, I would recommend a secondhand Dell OptiPlex system. MT, SFF or MFF system depending on your other components & hard drive requirements. These old Dell systems can be obtained from eBay and are relatively inexpensive.
You need to be aware that the Sandy Bridge HD2500 IGPU's don't support OS X, you need a CPU with a HD3000 IGPU if you want to use it to drive a display. Otherwise you will need an old discrete GPU for OS X Lion to work.
Only the higher end Ivy Bridge CPU's support macOS, i.e. drive a display, using the HD4000 IGPU. Otherwise you will need an old discrete GPU for OS X Mountain Lion to work.
A Haswell CPU with a HD4400 or HD4600 will work in Mavericks. The HD4400 isn't natively supported but a simple fake device ID can enable it to work.
There are a number of guides for these old Dell systems with Starter EFI's for Clover/Chimera. Not too many guides for these older OS's using OpenCore.