The "Dragon Box" game on iOS is a fascinating way of presenting "algebra" (isolating a variable in a linear equation). It starts with a very abstract presentation of the rules (using cards with monsters on them - gradually introducing the rules) and eventually subs in letters and numbers. I suspect it might also be useful for adults who've had anxiety and poor success with more formal approaches.
It's a progressive game, where you have to complete a puzzle to get access to the next one. One thing that was surprisingly effective at motivating my four year old boy (almost five) was that they change the appearance of a cartoon monster at the end of each puzzle (or every 2-3 puzzles). He kept wanting to do the next puzzle to see how it changed.
As a footnote to your comment, the Dragon Box game is available on Android as well, and there are actually a series of games for different age groups and different skills.
It's a progressive game, where you have to complete a puzzle to get access to the next one. One thing that was surprisingly effective at motivating my four year old boy (almost five) was that they change the appearance of a cartoon monster at the end of each puzzle (or every 2-3 puzzles). He kept wanting to do the next puzzle to see how it changed.