Hydra vs John’s Background Switcher

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.

John’s Background Switcher changes a Windows or Mac desktop background on a schedule, using individual photos or assembled montages and collages. Its image sources include local photos and services such as Flickr, SmugMug, Unsplash, Pixabay, Dropbox, OneDrive, Vladstudio, Immich, and Media RSS feeds, though availability varies by platform. Windows also lists Pexels, Last.fm, and Wallhaven. On Mac, it can manage multiple monitors, showing the same or different images on each, or using a single monitor. Mac switching intervals range from every 10 seconds to 7 days, with grayscale, sepia, and desaturation effects. Windows support starts at Windows 10 and requires Microsoft.NET 4.8; the setup wizard can install that dependency. The maker says settings and authentication tokens are stored locally, photo services are contacted directly, and cached photo results are kept for no more than two days. Windows is free at free. Mac direct costs 7.99 USD once, and Mac App Store costs 8.99 USD once.