I've recently launched Mashups.io - my own Yahoo Pipes tool.

https://www.mashups.io

And using the tool, I've been filtering, changing and tweaking various RSS feeds along the way.

I absolutely love RSS and absolutely loved Yahoo Pipes. For me, that got me into mashing up stuff on the web.

For devs, RSS feeds also provide a very easy way to source data. No need to get API keys and tokens, it gives you real life dataset immediately and easily. And from there, you can create tools.