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).