Data Sources - Not a formal integration point library, but a good place to add scripts used for Data Source Scripts. Read more about how they work here and here. The Source field simply references the script like script:/sitecore/system/Modules/PowerShell/Script Library/[MODULE NAME]/Data Sources/[SCRIPT NAME].
Event Handlers - Requires a patch file to enable the desired events. Read more about it here.
Functions - Exposes scripts to the command Import-Function.
ISE Plugins - Appears as a button in the ISE Settings tab.
List View - Represents the ribbon buttons such as for Actions and Exports.
Reports - Appears as a shortcut under Sitecore -> Reporting Tools -> PowerShell Reports.
Toolbox - Appears as a shortcut under Sitecore -> Toolbox. Visibility can be control using rules made available from within the Interactive field section.
Tasks - Not a formal integration point library, but a good place to add scripts used for Scheduled Tasks. SPE includes a PowerShellScriptCommand found under /sitecore/system/Tasks/Commands/PowerShellScriptCommand which is used to run scripts from within scheduled tasks.
Web API - Exposes scripts than can be consumed through SPE Remoting. The script can be executed by requesting a specific url.
Workflows - Not a formal integration point library, but a good place to add scripts used for Workflow Action Scripts. Read more about how they work here.
Remoting - Interact with SPE through the provided web services as described here. A Windows PowerShell module is made available to encapsulate the web service calls into PowerShell commands.
Some integrations need to be synced with the Core database through the ISE. See the Settings section of the Scripting documents for instructions.