Bolt
https://bolt.eu/en-gb/
This is probably the most popular app, with the most drivers. Until recently its been cash only. Some drivers may not accept the in app credit cards. The fares are also the cheapest!
Grab
https://www.grab.com/th/download/
Grab is a do everything app, from ordering food, to taxis. The Taxis in grab are less numerous and more expensive, but they always accept credit cards.
Movmi
https://muvmi.co/en
This is a ride sharing TukTuk for Bangkok areas only right now. You load the app and it shows you pick up and drop off spots in your small area. You can book 1-6 seats in an Electric TukTuk and they will route a tuktuk to come pick you up in a few minutes. This is a very inexpensive option, great when its not raining. Think of this as the last mile transportation from any BTS station.
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It's a good idea to have multiple taxi apps setup.
You can flag taxis down on the street, and most streets have motorbike taxi guys available too.