Ideas is a Salesforce standard feature where you can manage your ideas. Ideas have a voting mechanism where people can vote for an idea and leave comments.

The best example is the Salesforce idea website. Please feel free to post your ideas related to Salesforce features at https://success.salesforce.com/ideaSearch.

Chatter answers are similar to the self-service community where you can post questions and also answer them. People can like and comment on the answers or flag improper content. Based on the reputation earned by professionals who have answered and are active on the community, you can assign badges such as newbie, expert, and so on.

The best example for this is the success community, where you may want to post questions and get answers related to Salesforce administration and development. It is available at https://success.salesforce.com/answers.