Leap - With Leap you find things based on your natural memory of that file.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
Elyse - The free version allows up to 30 tags.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.