Squirro can be extended by creating Pipelets . These show up in the Custom section of the pipeline by default.
Finding Pipelets
Additional Pipelets can be added using the Plugin Repository.
Squirro Script
Squirro Script can be used anywhere in the pipelet and is listed as a custom step when installed.
Writing Pipelets
Creating Pipelets is a Developer capability. See Pipelets for documentation.