From the ashes of the popular CyanogenMod custom ROM, LineageOS has emerged as a worthy successor, providing users the same near stock experience with a few useful customization options. Now, Lineage is introducing an SDK in a bid to get developers building interesting things based on its own APIs.
The first public release is Ilama (API 9), and the project has some documentation on its Wiki to help devs get started. In its blog post, Lineage draws specific attention to two APIs: Styles and Profiles. The Styles API is linked to the system styles LineageOS got in version 15.1, and it makes possible the addition of an automatic dark mode to any app that incorporates it. It's a "painless global light/dark mode for everyone," according to Lineage.
With the Profiles API, developers will be able to trigger profile changes (that alter WiFi, Bluetooth, or volume settings) at a system level, which could be particularly useful for apps that interact with other IoT devices. The Lineage SDK is now rolling out, and developers can submit their own contributions to the open source gerrit, too. More information can be found on the Wiki or you can get involved with the conversation on Reddit.