The admins here will also often request that you ask one question per thread.
About your questions though:
[ol][li]Opus isn't a task scheduler or notification application - so I'm not as surprised as you are that nobody has asked for this. If there is some other reminder app you use or are aware of, it would likely be trivial to integrate it with Opus as long as it supports a command line interface of some kind to create new reminders. Come to think of it, you could also could create a file collection (Todo) and put files you want to come back to in it... you could then do a few things:
[ul][li]You could create a saved layout to open the 'Todo' collection, then set the Preferences / Launching Opus / Startup / Open a saved Lister layout option to load that layout.[/li]
[li]You could create a scheduled task using the built-in Windows Task Scheduler to run an Opus command to also open the 'Todo' file collection as the sort of reminder you wanted...[/li][/ul]
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[li]No... however, again - if you know of any calendaring app with a UI that you like with a command line interface that allows adding text to a calendar date, it can be integrated. Alternatively, you could also write something for the Opus double-click action (or possibly a script) that could add files/folders that you double click on to an Opus File Collection. You could set it up to create date based sub-collections to put the files and folders into. When you want to see what files and folders you accessed on a particular date - you could just go to that days folder in the collection and see what's in there. I recall there being some posts on the forum asking how to integrate Opus with various 'Recent' file/folder tracking applications. But on quick search, I couldn't find them again - and don't know that any of those apps had any sort of calendar view that might more closely match what you're looking for.
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[li]For me, the Preferences / Folder Tree / Options / Automatically expand to current folder / No content population option works the way you're asking...[/li][/ol]
If any of these option sound appealing enough to try and you need help setting it up, just shout back. Others may have other ideas of course...