A new "killer" app?

I was brainstorming about making some of my other development projects simpler, and I realized they mostly all come down to the same problem: I simply want to create lists of text or of files, apply tags or associate numerical values or notes or lonks to other files, and sort filter and color based on often-complex sets of criteria. I'm imagining something hopefully-simple that could manage all that; and it could be the core for managing todo lists, audio files, video clips, downloads, and so on. Yeah, it's another big dream...