Standalone applications follow one-tier architecture. Presentation, Business, and Database layer are in one system for a single user.
Client-server applications follow two-tier architecture. Presentation and Business layer are in a client system and Database layer on another server. It works majorly in Intranet.
Web server applications follow three-tier or n-tier architecture. The presentation layer is in a client system, a Business layer is in an application server and Database layer is in a Database server. It works both in Intranet and Internet.