Yes, you can call another Applet using the ChainApplet() method. See the Formativ language guide for more information. See below the comments from the language guide.
Utilities.ChainApplet = “Message Notes_flexalock”
Applet Chaining makes it possible to build interaction solutions based on two or more discrete Applets. Specify the applet you wish to chain by providing it’s name to the Utilities.ChainApplet property. Only the applet name needs to be supplied, though the full path may optionally be supplied. When the applet containing this line finishes executing, the applet indicated by Utilities.ChainApplet will be automatically executed (assuming the applet is available).
You can only specify one Chain Applet at a time. If your Applets makes two calls to ChainApplet, only the most recent call will take affect. The applet you specify in the Utilities.ChainApplet property does not get executed until the current applet finishes.
Formativ 2.0 also introduces the concept of Applet Data Exchange, which makes it easy for one applet to pass data to another via a global ‘scratch pad’. This feature can be used to pass data between Applets during chaining. See the TransferData property for more information.
On a separate note, you can also use the Formativ API (COM/XML based API) to interact with Formativ from processes external to GroupWise. See the URL below for more information.