How can I cancel an existing process from within another process?

There are multiple approaches for cancelling a process from any other process:
1. Use the Process Management Services plugin, as suggested by @mjmallet (Not OOB)
2. Use the "Set External PV Smart Service" (forum.appian.com/.../. You can have a boolean flag in your process. Then you can set it from another process. You can have a trigger which will execute when that boolean flag becomes true. You can use this in case you desire synchronous behavior.(But this is not OOB)
3. Another way, as suggested by @senthilar is to use Send/Receive Message combination. It is OOB. But its behavior is asynchronous.

There are multiple approaches for cancelling a process from any other process:
1. Use the Process Management Services plugin, as suggested by @mjmallet (Not OOB)
2. Use the "Set External PV Smart Service" (forum.appian.com/.../. You can have a boolean flag in your process. Then you can set it from another process. You can have a trigger which will execute when that boolean flag becomes true. You can use this in case you desire synchronous behavior.(But this is not OOB)
3. Another way, as suggested by @senthilar is to use Send/Receive Message combination. It is OOB. But its behavior is asynchronous.