I need a simple tool that will carry out some conditional checks periodically and give me a red/green status that I can use as an indication that something is wrong.

These are examples of checks that I would like to monitor automatically:

Does a row exist in a database that meets a certain criteria?

Does a file, with a maximum age, exist on some network share?

Does the response-body of a HTTP-request match a specific regex?

So basically, it would free me from checking these various indicators manually and just have a red/green dashboard that I could monitor.

I'm thinking something like this has got to exist in a ready-made solution.