Backdrops vs Hydra

Backdrops is a wallpaper app with curated collections and new wallpapers added regularly. Its team creates original designs for Android devices, including exclusive artwork available in the app. Users can submit wallpapers, artwork, or photos for review and possible placement in the Community section. Wall of the Day highlights a newly created design or a selected favorite. Google sign-in can sync favorites across devices, and favorites can be paired with Muzei to rotate on a chosen schedule. The app is available for Android, iOS, and macOS. The free plan costs nothing and includes ads, with in-app purchases available. Backdrops Pro costs $4.99, paid once and removes ads, permits saving Explore wallpapers, and includes a Pro Pack of exclusive backgrounds and future Pro features. The terms say purchases are non-refundable and limit sharing Backdrops-owned Explore wallpapers outside the app; saved copies are for personal use. The Google Play listing warns that regular use may consume substantial data and that carrier or internet charges may apply.

Hydra is a continuous integration service for projects based on Nix. It checks out project source periodically or continuously, builds it, runs tests, and produces reports. Work is organized into jobsets whose inputs can trigger builds when they change; jobsets can also depend on one another. Flake jobsets are supported when their outputs expose a hydraJobs attribute set. Jobs can produce packages, ISO images, or tarballs, and jobset inputs can use Git checkout sources. Hydra also provides a JSON API. It is aimed at Nix and NixOS package developers, not people who only need to use NixOS. Hydra is open source under GPL-3.0 and listed at free. It is self-hosted, with no hosted option listed, and running it is currently supported only on NixOS; the repository recommends the NixOS module for production. Flake evaluation is restricted from accessing files outside the Nix store. Some state is stored in the database, so backups are needed, and the wiki reports that hydra-queue-runner can sometimes leave queued builds unscheduled.