Background
Only Android devices that are licensed by the Open Headset Alliance contain the so called Google Apps. Usually people associate apps like Google Maps, Google Play Store, etc. with Android, but because of the open-source nature of Android, manufactures can sell Android devices without Google Apps and therefore avoid to pay the license fee.
Custom ROMs
At first cyanogenmod shipped it's ROM with pre-installed Google Apps. In September 2009 the founder of Cyanogen received a cease and desists letter from Google, demanding that the Google Apps not be included in the team's ROMs, since the ROM could be ported to devices which are not licensed to have the Google Apps.In turn, that would bypass the requirement for the devices to be licensed. For a few days, development on the ROM ceased, there were outcries from Android users all over the Internet, and many bloggers suspected Google had just shot itself in the foot.
Eventually, an alternate method was found, whereby Google Apps are not included in the ROM proper but the Google Apps which came with a device would be backed up by the device's custom recovery or another app, and then re-installed onto the device once the new ROM was flashed. This would therefore "Google-ify" one's ROM.
How to install Google Apps?
Generally speaking:
If root then:
- If possible: Install the Google Apps package for your Android version
- If not possible: Install ROM (if exists) with Google Framework.
