These days, cash is not the only currency accepted at some restaurants around the world.
Instead of paying with money, diners at a restaurant in Tokyo work for 50 minutes if they want a meal.
Restaurant Mirai Shokudo, or Future Eatery, gives customers the option of earning a free meal by serving dishes, clearing tables and performing other tasks.
Those who help out at the restaurant can either claim the meal for themselves, or pass on the free meal to anyone who might need one.
It is not the only restaurant that has come up with a quirky concept for a good cause. Here are some examples across the world, including Singapore.
1. Wrong order? It's for a purpose
At the Restaurant of Order Mistakes, customers do not complain if their food orders are mixed up.
This is because the restaurant is staffed by dementia patients in an effort to foster tolerance, empathy and acceptance towards them.
One customer who visited the pop-up restaurant in Roppongi, Tokyo, last September said she ordered a hamburger, but was served gyoza dumplings instead. Despite this, she tweeted that she enjoyed her meal.
Last year, the restaurant raised almost 13 million yen (S$155,000).
2. Free food made from scraps
Bread crumbs, overripe tomatoes and brown bananas are not thrown out at this restaurant in Milan, which reuses leftovers from supermarkets to feed the poor.
"I never thought these ingredients were waste," said Michelin-starred chef Massimo Bottura, who started the project in 2015, reported Reuters.
Unlike traditional soup kitchens that require guests to queue, his new restaurant Refettorio Ambrosiano serves its customers at the table instead.
While this means the number of guests is limited to 96, Mr Bottura says serving the poor at the table helps them regain their confidence and take back control of their lives.
3. Pay-as-you-wish cafe
Seniors are at the centre of this cafe in Bukit Batok, which opened last October.
They make up the volunteers who cook, brew and befriend other senior citizens who visit the cafe, called the Reach Community Cafe.
Customers can choose to pay what they want for orders, and the aim is to encourage seniors who live alone or are at risk of social isolation to interact and make new friends at the cafe.
The cafe is at Block 417, Bukit Batok West Avenue 4.
Eateries with a similar pay-as-you-wish theme can be found in several parts of the world, with the Reach Community Cafe inspired by the Japanese concept of Ibasho Cafe, which engages senior citizens in creating a multi-generational place.
4. Pay with Bitcoin, get free biryani
Cyptocurrency may have its naysayers, but not at this restaurant in Chennai.
Customers who pay for their meals in bitcoin are treated to free biryani, in an effort to encourage people to use the digital currency.
Calling bitcoin the "future of payments", restaurant owner Charan Raj told The Hindu in December that "the fact that its value is soaring is an added bonus".
So far, the restaurant has seen about 10 bitcoin transactions since last September.