I personally use the first two, in my roommate / office situation respectively. They work great, frankly. I have very few complaints about either.
If you can do it better, more power to you, but as with any crowded space, I have to ask, because I'm genuinely interested—why did you choose to start from scratch?
Ha, I'm aware this is a well populated space! I made this mostly as a learning experience for myself - I'm trying to improve my skills with Rails and I wanted to make something useful for my apartment and this is the result! I'm not trying to beat out any existing services by any means, just wanted to share my take on it.
Awesome, it's an excellent project to learn with. Simple data model, a clear problem, easily solved by a web app, with a high requirement for usability and simplicity. Glad to see your take on it too, keep it up!