Stride, Atlassian’s Slack competitor, opens its API to all developers 8 years ago
from Atlassian last earnings release in Oct 2017: "Trello continues to grow its user base at an impressive pace with more than 25 million registered users in over 100 countries, up from approximately 19 million at the start of the calendar year"
https://s2.q4cdn.com/141359120/files/doc_financials/Q12018/T...