MIUI is one of the most used Custom ROMs in the Android world thanks to its polished interface. Xiaomi, the Chinese company behind the MIUI Android Custom ROM, has decided to make the source code for their ROM and applications available to the masses via GitHub, the same git repository that the CyangenMod team uses.
They have started the open sourcing process by publishing the code to a few of the apps featured in MIUI. They will likely publish more in the very near future with open-sourcing the whole ROM too. It is great news for developers, since we would love to see some nice MIUI features in the other custom ROMs and Android too.