I built Competiwatch because I got tired of tracking my games in Google Sheets each competitive season. I wanted to add a new chart to my usual spreadsheet template and it was a pain because that's the nature of spreadsheets.
Competiwatch started as a web app that I hosted at my own expense. I wanted to use it myself and share it with friends, but I realized others wanted such a tool. Rather than host it forever or start charging users, I opted to rebuild it as a desktop app you run on your computer.
Any data you log in Competiwatch the web app, I have access to. I generally don't care about it, but I thought you should know that I can look at it if I want to. So don't put your passwords in the 'comment' field when logging a match, for example.
Signing into the web app via Battle.net lets me know you for-real have a Battle.net account. It also lets me use tools like the OWAPI to get your profile icon.
Data logged in the desktop app I do not have access to. Your data is stored on your computer.