Huginn

Huginn runs as a set of small agents, each one watching a source of information and acting on it without supervision. Agents can follow RSS feeds, watch web pages for changes, poll APIs, receive webhooks, send email and post to messaging services, and a scenario groups agents into a chain where one action triggers the next.

People use it to track price changes, competitor page updates, new job listings, backup failures or anything a plain webhook cannot easily cover.

Running it yourself means the sites you monitor and the notifications you receive are never handed to a third-party service, there is no account or per-run fee, and the database holds all of your agent history and is trivial to snapshot.