OpeningTree.Com and More
I find myself using openingtree.com about once a day now. Kids seem to like it. If you are smart enough to figure out how to use it, you should use it regularly. It should be pretty easy to use for a middle schooler or older, or advanced chess players in general. The only excuse for not using it, is you are good with ChessBase and you use it regularly (and this is like .01% of chess players that I know). Also Puzzle Storm on lichess.org is kind of fun for a few days, but I don't think I would recommend it as part of your routine.
