First let me say that I love the simplicity of this app but at times is a little bit too much.
One of my major gripes with it that it feels very "dated" in terms of modern practices.
For example - I cannot just "copy image" from my browser and paste it as a task/preview/ or in the chat. I have to manually download the image and upload it which is sooo 2010.

My second gripe is again with images - there is no way to see preview of the image as a thumbnail in the files or in the ToDo section. Which again, is very odd decision because everybody else has this function and also is much simple and clean to preview a image instead of having to click every single one.

My third gripe is browser notification. I don't know if it's just me, but I don't get native chrome browser notifications on my Laptop when something happens. I find this odd but it may be just me.

Suggestions -

1. Definitely think about the images implementation, for the moment this is a major, major drawback.

2, Recurrent (nagging) email reminders will skyrocket you to the league of apps like Todoist and such. Just google "nagging email notifications" - everybody loves them and still only handful of apps offer them, this is your chance to stand out from the crowd and give your future clients what they really want but almost nobody listened.

3. Keep it simple, I know that sounds weird after all my suggestions but I really do believe that you should keep it simple, just expand a little bit more, so the platform is more "user friendly"

Users love visuals, users love their reminders, that's what they want. They want something to remind them to finish their work, and not just once, but multiple times. Just look at the thousands of requests for such features at Microsoft ToDo's

https://todo.uservoice.com/forums/597175-feature-suggestions/suggestions/20366137-more-options-for-recurring-events

And for almost 3 years nobody listened. You can snag a big chunk of that userbase if you take advantage of this situation :)

Anyways, keep the good work and good luck! :)