Just like Hong Kong (Octopus), Seoul (T-Money) and London (Oyster), Singapore has a public transport card (Ez-Link). Like HK and Seoul, you can use this card for small payments in 7/11 alike shops.
This payment card works on all transport modes. Bus. MRT (metro). No matter who operates it.
Sadly it doesn’t work on taxis though.
Nonetheless. With a bunch of different players (SMRT, SBS, any other? But the same is true for London — and they have more players on the market) they have one simple unified payment system (and prices are the same no matter who is operating).
Why is this not possible in Belgium? Don’t get me started on MOBIB. “In order to travel validly on the networks of the various operators, you will need to store a valid transport tickets on your MOBIB card for each of the mobility operators you intend to travel with.” That’s a joke.