I wanted to find something similar for math, just to review and keep myself fluent because I want to eventually go deeper with physics, so I searched around and all I could find was Brilliant.
I did a bunch of the samplers they offer but this didn't really give me an idea of whether it's good or not, I really wish they had a trial or ad supported version or something like that because they basically strong arm you into putting down $100 unless you want to pay 2x or 4x per month for shorter time periods... I just don't know if I want it yet or not, so I can't justify that.
What is other people's experience with this thing? Is it worth it? Are there alternatives that are similar to Duolingo (keeps a streak, is gamified, cut graphics, with bite-sized levels, etc.)?
[p.s. I'm not interested in Khan Academy, it's slow, imperfect and MIT has lectures up for all of these topics when I want them.]
For more of a info-tainment / puzzle solving type of diffused learning - sure, why not? You can always try it for a month and see if you like it yourself. I wasn't a huge fan but I didn't like Duolingo that much either.
But still, as with everything, you're probably better off going to the library.