This is an essentially infinite number of letter-replacement puzzles. You know, the sort of thing you find in newspapers, where you have to deduce which number corresponds to which letter. Think "codewords" if you read The Times, but without the crossing out. So if you like that sort of thing, this is the sort of thing you'll love. For a start, it's essentially infinite.
DCode is totally safe for downloading. The game has been originally designed by Apposite Software and it is listed among the Puzzle Games category. This application was downloaded and installed by over 5 users and its latest stable release was on Apr 24, 2015.