In an unprecedented move, Google has pushed code for a Developer Preview version of Android to AOSP for developers to tinker with (for that matter, Google's release of the preview build itself at I/O was unprecedented). The Android L source code was pushed for the following devices:


Naturally, we expect these devices to be have custom ROMs available within days, but I should note that the source isn't anywhere near final so we shouldn't expect the typical stock-plus experience. Some apps won't work on this preview build (in other words, while running an Android L-based ROM, let's please not 1-star an app in the Play Store because it's not working properly). Also, the ROMs themselves will likely have many bugs, as the source code itself surely does (so we shouldn't blame the ROM developers for bugs that are no fault of their own).

EDIT: as noted by Android Authority, only some GPL-licensed parts of the source code were released, from which it is impossible to compile a working build.

Speaking of custom ROMs, don't expect CyanogenMod 12 any time soon. The CyanogenMod blog already weighed in, saying they won't be building CM12 based on this very pre-release code. Understandably, they don't want to attach the CyanogenMod name to builds based on pre-release Android code that could change drastically between now and final release. That said, they are definitely taking a look at the code and we could see a full-featured CM12 build very shortly after Google pushes final code to AOSP.

Source: Google's Android Git, h/t Phandroid