WeWard, an app that offers real-world rewards for walking, announced Wednesday it’s signed tennis champ Venus Williams as an investor and ambassador for the app.

The app, which offers users points called Wards for steps taken, lets users track their movements or import pedometer data from tools like iPhone’s Apple Health, Android’s Google Fit, or Fitbit. When they’ve racked up enough Wards, they can be redeemed for gift cards, charitable donations, or even cash deposits to user bank accounts.

“We’ve decided to do something very simple,” says cofounder and CEO Yves Benchimol. “We just give cash to people to walk.”

In addition to tangible rewards, users can also collect virtual trading cards scattered at particular places on the map in a manner familiar to players of games like Pokémon Go, encouraging people to explore their surroundings on foot while racking up steps. About 6.5 million of the cards, dubbed WeCards, are collected every day.

Users can also compete with friends, or within virtual leagues based on their activity levels, tracking their performance on virtual leaderboards and receiving virtual gold, silver, and bronze medals based on their rankings. The app has also hosted competitions around regions and countries, centered around events like the Olympics or Super Bowl, where players’ steps are added to totals for their locations.

“Some people are way motivated by beating their friends and compete with their friends,” Benchimol says. “Others want to beat all the community.”

So far, WeWard has distributed $20 million to its users and generated $1 million in charitable donations, according to the company. With the Venus Williams deal, users will be able to access special challenges and rewards linked to the tennis player, including sports tickets and Garmin watches.