First of all their is no replacement for quora. It is a one of a kind platform for sharing, discussing ideas and experiences. It enables people to connect with one another in such a meaningful and deep way that I don't think no other community website comes close to it. Yet there are certain websites which are similar to quora.
Reddit This site is very similar to quora with a very large user Base. Some may argue that it's better than quora but again it depends on the individual.
Yahoo answers Before quora became popular. This was THE platform for people to communicate and exchange ideas. Though it has lost its former glory it's still very much active with sizeable user Base.
Your story Though this site is more of a news board rather than an interactive community platform, it has really good content. Definitely worth a click.
Curiosity As their catch phrase suggests, the site really tries to makes u smarter with great content quality but some what limited interaction still a good site to spend your valuable time with.
Meet up This one needs no introduction. As the name suggests it is meant for “meetups” for members sharing common interests and forming their own online / offline communities.