It doesn't work by installing "apps", but rather, the whole system image is built from _your_ code. Which makes sense on a device that has 64KB RAM.
Any code samples they provide are just that: Samples.
If what you're looking for is a general public oriented device, this is not it. There's plenty in the market to pick from.
[1] https://wiki.pine64.org/wiki/InfiniTime
[2] https://github.com/daniel-thompson/wasp-os