What are some alternatives?
When comparing Vikunja and Zenkit, you can also consider the following products
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
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.
Wekan - The open-source Trello-like kanban (built with Meteor)
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Meistertask - MeisterTask is an intuitive task management and collaboration tool.