What are some alternatives?
When comparing Vikunja and OneNote, you can also consider the following products
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
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.
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.
Wekan - The open-source Trello-like kanban (built with Meteor)
Simplenote - The simplest way to keep notes. Light, clean, and free. Simplenote is now available for iOS, Android, Mac, and the web.