I would really like an offline tool where my data stays with me. I do not feel comfortable if someone else knows everything about my life. It is a major privacy

I would really like an offline tool where my data stays with me. I do not feel comfortable if someone else knows everything about my life. It is a major privacy problem. I would not pay for it though (unless it is flawless and <5€). And it would need to be Win & Linux, and easy to transfer/sync (manually). Of course it would need to support custom fields.