exit() is worst: in winForm, it's generally better to catch the exception on top level and show a MsgBox to the user without crashing. The user understand that his current action has failed, but he do not lost its input.
Look great! I wanted to see more on the calendar it self, but I have not found the demo link on the main page. IMO, you should add a presentation of your calendar without requiring to create an account.
Then, I've quickly read the part on concurrent programming. But I've not understood how it is easier with Pony. It's very frustrating. So far, my understanding is there is class (called actor) that can discuss together by sending each other immutable object. I would like to see some code in the tutorial that show how concurrency is easily done in Pony.
Don't forget the steam queue. It use prediction to show games that correspond to your taste. It's not very accurate, but it allow to show new games on each iteration. You do not waste your time on the always same top 100 games. It allow to discover some strange or underated titles .
I was also hoping a free hosting for my week-end projects. It would allow me to try the service, and maybe, become an evangelist inside my company.
Currently, while there is a free issue management in GitHub or BitBucket, these systems are too light. JIRA would have been great, but there is no way I pay when I do hobbit projects. IMO, a good way to do that is to be free for project with less than 3 users. Or have the first 3 users free, once the project team grows, there is no more choice than to pay :)