Contact
One inbox, read by a human. There is no contact form because a form would need a server, and this site does not have one.
Write to hello@pikkit.app.
Reporting a bug
The most useful reports say which tool, which browser and version, and what you expected to happen. If a file failed to compress, tell us the format and roughly how large it was — do not send the file itself.
Requesting a tool
Tell us the job, not the feature. “I need to split a class of 28 into groups of 4” is easier to build for than “add a grouping option”.