I used General Task in their beta and found it a great product, but I wasn't ready for it. Today I had the exact use case of a product like General Task, so I went to log back into my account and learned they're only providing the app as a self-hosted open-source project. I'm a little bummed.
General Task provided a great interfacing layer between my task sources (e.g., Linear) and my calendar (which could also be considered a task source). This made planning my day super easy since tasks beg to be shaped into a block of time. If a task isn't scheduled for a block of time, and only lives as a due date, it's easy to ignore it. General Task made that solid connection.
Best wishes to the team. If they ever bring back a hosted version and I still haven't filled the gap their product fit, then I'll be excited. It will also be interesting to see what else this team might bring to market.