SideNotes is described as 'Clean and handy notes on your monitor side' and is an app in the Office & Productivity category. There are more than 100 alternatives to SideNotes for a variety of platforms, including Windows, Mac, Android, iPhone and Online / Web-based. The best alternative is Joplin, which is both free and Open Source. Other great apps like SideNotes are Standard Notes (Freemium, Open Source), Notion (Freemium), Google Keep (Free) and Microsoft OneNote (Freemium).
Notebook PEAs - encryption of notes. Protects your private notes with a password. The text is never stored unencrypted on your disk (until you explicitly decide to do that). The used cryptographic primitives are currently considered as safe as possible.
File system notes is modern notes manager on steroids for macOS and iOS. Application respects open formats: plain/text, markdown, rtf, and stores data in file system. You can view, edit, copy data in favourite external editor and see live results in FSNotes.
Drafts, where text starts. Quickly capture text and send it almost anywhere! Drafts lets you turn text into action – it’s a quick notebook, handy editor, and writing automation tool, all in one. Open it and write right away, and create.
NoteAway is the simplest, most convenient way to take quick notes on OS X. NoteAway has lots of powerful features for free, like iCloud syncing, rich text, attachments, simple import/export, and a variety of customizable options.