Yes, it is definitely possible to build a simple web app with the functionalities you mentioned using Google Apps Script.
Here are the steps you can follow to create a web app:
Create a new Google Spreadsheet and set up the layout to match your prototype. You can add the necessary columns for goals, checkboxes, and user information.
In the same Google Spreadsheet, go to the "Tools" menu and select "Script editor" to open a new script project in Google Apps Script.
Write the necessary functions to send emails or SMS messages and communicate through Google Chat. You can use the GmailApp or MailApp service in Google Apps Script to send emails, and Twilio or another SMS gateway service to send SMS messages.
Create a new HTML file in the Google Apps Script project, which will contain the UI for your web app. You can use HTML and CSS to create the layout and style of the web app.
In the HTML file, create forms for users to enter their information and for them to update their progress. You can use Javascript to make the forms interactive and update the spreadsheet.
Publish your web app by going to the "Publish" menu and selecting "Deploy as web app". Choose to deploy the latest code and select "Anyone, even anonymous" for the "Who has access to the app" option.
Once you've published your web app, share the link with your users, and they will be able to access the app without needing to install any third-party extensions or apps.
It's important to note that you will need to write code to ensure the privacy and security of the user's information, and it's recommended to thoroughly test the app before sharing it with your users.
Overall, Google Apps Script is a powerful tool that can help you build simple web apps with minimal coding, and the best part is that it's completely free to use.
Regards,