Why would I choose Space over Upsource, YouTrack, and TeamCity? Follow

Space is an Integrated Team Environment that includes not only software development-oriented tools, such as code review, issue tracking, and continuous integration, but also a team directory, calendars, HR tools, a knowledge base, messaging, and many other features for various roles in a company. It is a complete solution provided as a service or hosted on site (planned for 2021), and it requires little to no integration with other software products that have similar functionality while still providing support for third-party products.

Upsource, YouTrack, and TeamCity, while they can be integrated together, are also standalone products that can be used with many different solutions.