Mixplorer - aka MiX, the only file explorer I’ve ever needed. It’s intuitive enough for basic file browsing, but it can do heavy lifting tasks. I exclusively move files on and off my phone by starting an FTP server.
Pulsar - One of the only apps I’ve ever paid for, it’s a music player that does everything I want and nothing I don’t. I’m one of those nuts who still maintains a personal library of thousands of songs rather than using spotify or whatever.
MS Swiftkey Keyboard - I went looking for this when Swype was finally discontinued. Gesture typing wasn’t common yet and I still find google’s stock keyboard absolutely insufferable. Swiftkey lets me adjust the size and layout of the keyboard with far less restriction.