To me the help sections is pretty clear. See http://askubuntu.com/help/on-topic
Copied from there:
We welcome questions about:
- Using and administering Ubuntu, including official Ubuntu derivatives.
- Running third-party applications on Ubuntu.
- Development on Ubuntu.
- Services provided by Ubuntu
- Any question not mentioned below or here are great! There are no "dumb" questions!
This is not the right place for:
- Linux Mint, Backtrack, Gnome-Remix (prior to 13.04) and other Linux distributions (try our friends at Unix & Linux Stack Exchange).
- Bug reports (How do I submit a bug?).
- Issues with the next version of Ubuntu (Ubuntu+1) (More information about Alpha and Beta release issues).
- Shopping Recommendations
- Support of versions for Ubuntu releases past "End of Life" (EOL)
From the link:
Recognised Ubuntu flavours
These are derivatives that use Ubuntu as their foundation and contribute significantly towards the project.
- Edubuntu — Ubuntu for education
- Ubuntu GNOME — Ubuntu with the GNOME desktop environment
- Kubuntu — Ubuntu with the K Desktop environment
- UbuntuKylin — Ubuntu localised for China
- Lubuntu — Ubuntu that uses LXDE
- Mythbuntu — Designed for creating a home theatre PC with MythTV
- Ubuntu Studio — Designed for multimedia editing and creation
- Xubuntu — Ubuntu with the XFCE desktop environment