TaskSpark is built by one person. Every message arrives in a real inbox and gets a real reply, usually within a day or two.
Bug reports. The more detail, the better, what you did, what you expected, what happened. Screenshots help. Version number is in the bottom-right of the app.
Feature ideas. Tell me the problem you're trying to solve, not just the solution. Half the best features came from "I was trying to X and it was weird that Y…"
Nice notes. These keep me going. Send them.