Here's my feedback. As a part of a small startup team, I used Jira for years before Github issues and Slack were there.
The company I work at right now still uses Atlassian's trio Jira + Hipchat + Bitbucket. They are great tools with lots of features but Jira's productivity is much slower compared to Github issues and Hipchat offers a poor user experience compared to Slack.
Productivity apps are never in top 10 on app store. The efforts you spent building your app did not pay, but I don't think you should blame app store for that.
I would suggest not to take it as a failure of the mobile app concept. Learn form your experience and think about what you can improve.
I agree that closing all borders physically would be tough. There would be controls on the roads and airports, but in the zone you posted a physical wall is required to isolate two countries.
I agree. I used "favorites" to bookmark something interesting, to be able to find the information if no time to read. But putting to favorite doesn't mean I like the content. I can favourite a tweet with a link to some bad news, such as shutting down a business, economy getting worse etc. I don't really "like" the tweet, it's just a interesting fact and I want to bookmark it as "favorite".
As a designer I love the equal positioning that flexbox offers. I tried to use it for some projects, but it needs some more work on browsers compatibility.
I like the animations, inputs are really what I need today for my UI designs.
Checkboxes have different styles in Chrome and Safari. Safari checkboxes look a bit weird as in unchecked mode a rotated green tick is displayed inside a checkbox, and in checked mode one of the tick's lines extends horisontally.
In Chrome the checkbox looks really nice though.