• Apps > App manager
• Search IntActApp
• Click on Install

Download the release jar or compile it to obtain intactApp.jar.
Then to install it:

• from Cytoscape
  • Open Cytoscape
  • Apps > App manager > Install from file ...
  • Select intactApp.jar
• from system
  • Place intactApp.jar in ~/CytoscapeConfiguration/3/apps/installed/