If, as we saw in Transfer in Chess Learning, chess doesn't make you smarter, what does? Let's ask Google.
Chocolate makes you smarter. So does exercise, running, travel, and reading.
Seven hobbies that make you smarter: '1. Play a musical instrument. 2. Read anything. [...] 6. Work out your brain. ('sudoku, puzzles, riddles, board games, ...') 7. Meditate.' Board games? Yay for chess!
Thirty killer apps: '1. Casual. 2. Fooducate. 3. Cloudswave. [...] 29. ATracker 30. Timely.' Killer apps will make you smarter every time.
Riding centuries: 'a bicycle ride of 100 miles (160.9 km) or more within 12 hours'. That sounds the same as exercise and running.
Google autocomplete (as in Google Autocompletes CIS, March 2015): Reading makes you smarter; Exercise makes you smarter. We knew that already, but what about these: weed, dancing, music, Mozart, beer, coffee, TV.
Google also points to Cracked.com's 5 Things You Didn't Know Could Make You Smarter: '1. Electricity to the Skull 2. Cigarettes 3. Dancing 4. Being in a Terrible Mood 5. What You're Wearing'
Lists definitely make you smarter. In short, everything makes you smarter, except maybe blogging. Or reading blogs.