Oracle Equivalent of PostgreSQL CLUSTER PostgreSQL has the CLUSTER command to group rows physically on disk. By grouping on information where "neighboring" rows (for lack of a better term) are often accessed together, performance improves since fewer disk blocks need to be read in a given query. Does Oracle have anything similar? Would it even help performance on a large table that is almost never updated if there is such an option?
Similar concept in Oracle is called Index-Organized Tables (IOT).

Difference with PostgreSQL CLUSTER is that in PostgreSQL CLUSTER command reorganizes table once and later table still grows as it wants to. In Oracle IOT keeps its structure as ordered by index.

Unlike Phil I'm seeing IOTs now and then. The most often they are used when you need to retrieve many (think hundreds) rows by index.