Android 8.0 (Oreo) is finally beginning to make its way out to devices outside of the Pixel and Nexus range thanks to the coordinated efforts of the custom ROM development community, and the folks at XDA Developers have taken it upon themselves to begin curating a constantly updated list of devices that have such ROMs available. The list includes phones from a wide variety of manufacturers, almost none of which have put out any official Oreo sources yet. This means that the AOSP Oreo and Lineage OS 15 ROMs that are featured are built from the ground up by dedicated community members, and thanks to proprietary bits of code in some phones' hardware drivers and other bits, may not work completely at this time. It should go without saying, at this point, that most of these ROMs will not be suitable as daily drivers.
ASUS faithful who have a ZenFone 5 can try out an AOSP build of Oreo, while Lineage OS 15 has been built out by two different community members for the ZenFone 2 laser. Moto device owners with either a 2015 Moto E, 2014 Moto X, or any Moto G besides the newest can all flash Lineage OS 15, as well as owners of the Lenovo Vibe K5 Plus. Samsung Galaxy S6 owners are on the list, but there are no other Galaxy phones in on the Oreo action for now; just the Galaxy Tab S2, and the 2014 version of the Galaxy Note 10.1. Sony's Xperia device range sees Oreo ROMs for the Xperia M2, Xperia SP, and the Xperia T, TX, and V.
OnePlus is a standout on the list; every single device that the OEM has ever made has a version of Oreo available, though no OnePlus devices have both AOSP and Lineage versions to choose from. Xiaomi is another standout, with 10 devices in total on the list, with three from the budget Redmi range, the Mi Max, and six flagship Mi series phones, all the way back to the Mi 3. Finally, owners of the 32 bit Nexus 6 and Nexus 5 are on the list, but that's where the list ends; Nexus 5X and 6P owners aren't included since they get the update officially, and owners of the Nexus 4 and older hardware don't have Oreo just yet, and may well not get it simply due to the age of their hardware.