San Francisco public transit riders are finally getting a mobile app for buying tickets. Today, San Francisco’s Municipal Transportation Agency officially launched an app called MuniMobile for iOS and Android.

The app was first promised in January and expected to debut over the summer; however, now is the first time the app is being made available broadly. Riders will be able to pay for fares with a credit card or PayPal using a smartphone.

The new app is aimed at casual riders and tourists, who don’t have an easy way to purchase tickets. Previously, San Francisco’s Municipal Transportation Agency only allowed people to buy individual tickets with cash through terminals located at stations or from the operator of the bus or train. Through MuniMobile, smartphone users will be able to purchase and store single tickets as well as one-day, three-day, and five-day passes for multiple people.

Already, regular Muni riders have a program called Clipper that allows people to store tickets, monthly passes, and cash fares on a reusable card. Users can reload their cards with funds online, but to the dismay of some they aren’t able to renew or store monthly passes via the MuniMobile app.

The new app comes as other cities are revamping their transit fare payment programs. Earlier this year, the London Underground enabled its transit system to use Apple Pay to pay for rides. Meanwhile, New Jersey Transit, Virginia Rail Express, and the Los Angeles Department of Transportation have all upgraded their fare systems to accept PayPal.

The reason these transit systems are opting for mobile payments is to cut down on the difficulty of entering payment information on a phone.

For companies like Apple, PayPal, and Google, transit apps represent an opportunity to get more people using mobile payments. So far, people have been slow to adopt mobile payment technology like Apple Pay. In a recent study, payments analyst PYMNTS noted that only 16 percent of people with an iPhone 6 or 6s have tried Apple Pay; an even smaller number use it regularly.

Still, in-app purchases remain an important use case for mobile payment technology, and it’s likely that companies invested in this arena are all gunning to be the mobile payment app of choice.