It looks like you started Diaspora two times.
First make sure to you have Diaspora and your other projects alongside each other, not nested.
~/Diaspora
~/Projects
Then change into your projects folder, get the latest version of Rails and create a new project:
cd ~/Projects
gem install rails
rails new project2
cd project2
bundle install
There start your other project first:
cd ~/Projects/project2
bundle exec rails server -p 3002
Now in a second shell start Diaspora:
cd ~/Diaspora
bundle exec rails server -p 3001
Make sure to use bundle exec
to avoid any version conflicts between the gems Diaspora uses and the gems your new application uses.