Mark the countries you have visited and see your count and share of the world - here in this tab, with nothing uploaded.
A travel map is a record of where you have been - which is exactly the kind of thing travel apps keep. This one keeps nothing: it is drawn in your browser and your list stays on your computer.
Out of 195: the 193 United Nations members plus the Holy See and Palestine. Territories such as Greenland or Puerto Rico can be coloured but do not count as countries.
Copy the list from the box - it is plain text - and paste it back in later. Nothing is stored on this site, so nothing can be lost or leaked from it either.
Yes - the line under the map shows how many countries you have visited on each continent.
Yes, for anything, commercial work included. The map data is public domain (Natural Earth and the US Census Bureau); there is no watermark and no credit required.