Chandler is an open source organizer which lets you create and save notes and organize them in your calendar.
Although at first I found the interface a little cluttered, it really seems to have everything you need.
The quick entry section at the top, which you could mistake for a search bar, lets you create notes quickly. Detail on your notes is shown on the right side of the interface.
Chandler also displays a calendar, which you can browse through to see notes for each day.
In place of tags, Chandler has what it calls collections.
These work more or less the same way, however I've found them to be slightly less flexible.
Chandler allows you to easily import and export information, mostly as CSV files and you can share your notes with others, by using the Chandler Server and Hub Sharing Service.
One of the best features of Chandler is that you can customize it with any sort of plugins found on the website.
Despite a slightly cluttered interface, Chandler is a solid open source note taker and organizer.