The features that must have

Questions

Create, show and edit
vote system: up | down
syntax highlight using a js lib

Answers

Create, show and edit
vote system: up | down
Select an answer as the best

User

Create, Show and edit
Avatar
Basic Reward points system
Basic Statistics

Tags

Creation and association to questions
Search using tags

Flags

Flags for questions and answers

Feedback

Basic feedback system

Admin

Moderation on questions,answers and users

Search

Basic Search on questions

i18n

Integrate rails-i18n

Nor required, but planned.

Comments

Create Show and Edit
flags
Admin moderation

Search

Improves

oAuth

User

Improve Profile

Trends/Statistics

Badges

Syntax Highlight

Using GNU/source-highlight processor