I started playing with a new app called Alarms yesterday, and it's already become indispensable to me. It's rare that something fits so perfectly into my workflow that I don't think twice about the space it takes up in my (already frighteningly crowded) menubar. What is it, you ask? It's an unobtrusive means of scheduling tasks on a timeline, seeing your upcoming tasks and taking care of things one at a time.
Alarms isn't a replacement for a full-fledged task management system, but it's perfect for remembering to reply to emails that you aren't ready to tackle at the moment, honey-do items, turning the fish filter back on 10 minutes after feeding anything that just needs a gentle reminder at a specific time.