Obyte is the platform that hosts all this.
Byte is the native currency of the platform, it is used to pay for fees. It is also the most popular and the most widely distributed asset on the platform (there are many others, see Tokens).
GBYTE is the currency unit of Bytes that is traded on exchanges, 1 GBYTE is 1 billion Bytes. While Byte is the smallest indivisible currency unit, GBYTE is more convenient for expressing the most common amounts, and amounts in GBYTE are fractional numbers with up to 9 decimal places. Byte to GBYTE is what cent is to dollar, or satoshi to Bitcoin. GBYTE is sometimes abbreviated as GB. Some apps use MBYTE (or MB) which is 1 million Bytes. We use other SI prefixes as well: KBYTE (KB) for 1000 bytes, TB for terabyte (1 trillion Bytes).