You don't give us too much here...
You can develop something in JavaScript using a third library like SharepointPlus with the createFile function
You'll do:
$SP().createFile({
content: JSON.stringify(strJson),
destination: "http://mysite/Shared Documents/file.txt",
url:"http://mysite/",
after:function() {
alert("File saved");
}
});
The createFile
of SharepointPlus uses the CopyIntoItems web service of Sharepoint.