I am current using a software call Thing. unfortunately, this software only work on MAC. Now I am looking for similar software for PC. Any recommendation?
Well, you might want to try a web based tool. The main benefit here is that you can access it from everywhere without having to install anything on your machine (so it's going to work both on Window, Mac, Linux or anything).
I'm currently telling more about what TaskWriter can do for you at TaskWriter - Productivity Your Way, but it's still work in progress, so do not hesitate to ask me directly for anything.
For years I used Palm OS smartphones, and at least have the reason I stuck to the platform was for the simplicity and flexibility of the Palm Desktop client, which features an excellent categorized task list manager, not to mention equally robust calendar and memo functions. You can download it for free and use it even if you have no intention of syncing to a Palm device. It's something that never occurred to me to use as standalone software until Davidco coach Kelly Forrister recommended it on a podcast.