http://orgmode.org/Org mode is an emacs extension that defines a plain-text format in which you can take notes. It also includes a rather extensive system to manage and schedule tasks and todos (cf. the "Org Agenda").
It has a rather steep learning curve however, especially if you're new to emacs too. From what I know about it so far, I really like the premise and philosophy behind it, but I haven't managed to fully switch to an org-based setup for scheduling yet.
I would also be interested in what others here use to access/modify their schedule. Since I can't use Emacs for work, an option to quickly access it from my phone would be rather crucial, and the options I've found so far are mostly quite minimalistic...
I'm thinking some (basic) self-hosted, web-based tooling to manage the schedule in a Git-Repo would be very useful.