I have to give Pat Vachon (mBlazonry) a lot of credit for coming up with this awesome and stupidly easy-to-implement idea!
By adding a UI-only formula field to a parent model and using the syntax below in the UI formula builder…you can calculate and display rollup summaries.
Just be sure to add the child relationship to your model within the model’s fields section.
No Master-Detail relationship needed (lookups relationships are fine)
No third-party app needed like DLRS (declarative rollup summaries) or Rollup Helper
Usable directly in a basic model on field editors, tables, templates, page titles…no need to build a separate aggregate model
Granted…this is a UI-only field, so the summary isn’t saved to the object, but you could easily solve that with an action sequence that would 1) update a SF field with the UI-only value and 2) save down the value
Super quick and easy to implement
table with drawers that open up to display the specific goals