Ghostnote is described as 'adds contextual notes to almost anything on your mac. Add notes & todos to folders, applications, open documents, even websites. Think about it as post-it-notes for your OS' and is an app in the Office & Productivity category. There are more than 100 alternatives to Ghostnote for a variety of platforms, including Windows, Mac, Online / Web-based, Android and iPhone. The best alternative is Joplin, which is both free and Open Source. Other great apps like Ghostnote are Standard Notes (Freemium, Open Source), Google Keep (Free), Microsoft OneNote (Freemium) and Evernote (Freemium).
Notational Velocity is a mouseless application for storing and retrieving notes. With Notational Velocity, searching for notes is not a separate action; rather, it is the primary interface. Searching encompasses all notes content and occurs instantly with each key pressed.
NixNote, formerly Nevernote, is an open source client for Evernote . It is written in Java so it will also run on Windows & OS-X, but the primary focus has been to try and get a usable environment for Linux.
ColorNote is a simple notepad app. It give you a quick and simple notepad editing experience when you write notes, email, message, shopping lists and todo lists. ColorNote makes taking a note easier than any other notepad apps.
myBase is a unique free-form database software that allows entry of unstructured text, webpages, images, documents, emails and even arbitrary files without regard to length or format. All information is automatically compressed and stored in the tree structured outline form.
A simplified, RedNotebook-type journal/diary app. With a focus on minimal design and a distraction free writing environment. Makes a folder full of dated text files that are easy to access even without the journal program.
Keepmark allows you to organize your files, documents, emails, bookmarks, tasks and generally - resources. Its also an efficient solution for finding your resources by names, meta-data and document content.