I use vimwiki and wrote a bash script that pulls all of the Todo items from across my wiki and puts them in a single file with TODO and IN PROGRESS sections.
I have a keybind that pulls up the list and runs the script to refresh it.
It's not linked to any calendar though. I keep my to-do list and calendar separate.
I use Gmail and have that calendar for my personal stuff. At work I am forced to use outlook.