I believe Llama is open source but not sure how complicated it is to get running locally. Nevermind: https://replicate.com/blog/run-llama-locally
You can probably write a bash wrapper around it that feeds in "Can you summarize this text: (text here)" by setting the PROMPT variable the bash script. (Probably just do PROMPT="Can you summarize this text: $1") (Obviously don't recompile everytime so remove the clone build and download code)
App seems nice and I have no complaints with it but it's not FOSS and it has ads. It would be cool if there were easy ways to make revenue off of FOSS that dosen't rely on donations so I understand why it would be proprietary.