They are similar. They don't affect overall system capacity other than max sessions allowed. AMP-less / PE-only are two names for the same thing.
These are server nodes connected via BYNET but with no (external) disk. The purpose is to allow more total concurrent sessions to be connected (by defining additional PEs beyond the default of 2 per normal database node), or provide more network throughput beyond the default of one gateway and adapter (pair) per per normal database node, or to provide mainframe connectivity ( FICON node).
The term "application node" is an older name for what is now generally called a Teradata Managed Server. It is a server provided by Teradata that is not running Teradata database software.
Think of a Service WorkStation (SWS) as a "hardware console" used by Teradata Customer Support.