Indefinite pronouns can indeed replace nouns in various grammatical roles:
* Subjects: "Someone is knocking on the door."
* Predicate Nominatives: "The winner is everyone who participated."
* Direct Objects: "I saw something strange in the attic."
* Indirect Objects: "She gave everyone a piece of cake."
* Objects of Prepositions: "They talked about nothing important."
* Appositives: "My neighbor, whoever it is, is making a lot of noise."
Examples of Indefinite Pronouns:
* Singular: someone, anyone, no one, everyone, everything, something, anything, nothing, each, either, neither
* Plural: some, any, none, all, both, few, many, several
Let me know if you'd like to see more examples!