The vogue for brain training is quite astonishing. For example, the biggest vendor of such tools, Luminosity, claims over 70 million users in 182 countries. The problem is that independent, scientific evidence is scant to back-up the claims of most commercial vendors of "cognitive development" apps.
A notable exception appears to be "dual n-back" training. You can try a version of this for free here: http://www.soakyourhead.com/
The idea is that, whether multiplying 27x14 in your head, or devising a new strategy or career direction, you are loading up your working memory. If that can be beefed up, it has positive, measurable, consequences for your IQ (10-20 points within three weeks), and, related, your performance on a host of cognitive challenges.
But it's not just working memory training that has proven results. The evidence is pretty strong for cognitive benefits across the general population from improved diet, exercise and sleep. Nootropics (drugs for mental clarity) ,such as piracetam and noopept, also have reasonable support, as does Trans-Cranial Stimulation with a weak electric current (albeit more so for structured and quantitative tasks).
So, put these proven "brain training" interventions together with improved training in other areas - such as creative or critical thinking - and you have a recipe for rapid improvement in cognitive skills. For some of us, it's a mystery that such evidence-based techniques are not in widespread, full-powered use.