I'm only a relatively casual user, but doesn't Atlassian mostly buy and then manage existing software products? They didn't develop Trello, HipChat, Bitbucket etc.
Every time I run into an issue with Atlassian software, I find a JIRA ticket from 7 years ago. If they have a capable dev team, it's probably working on projects off my radar?
A lot of people would say Google these days... now that they're starting to move beyond Material Design 1.0 a lot of their products are becoming more visually mature and unique, along with their substantial investment in machine learning to make their software more personalized, etc.