hollr is described as 'small, privacy focused, event management service where you can easily create and share events with a group of friends. No registration required' and is an website in the Office & Productivity category. There are more than 10 alternatives to hollr, not only websites but also apps for a variety of platforms, including iPhone, Android, iPad and Android Tablet. The best alternative is Meetup, which is free. Other great sites and apps similar to hollr are Get Together (Free, Open Source), Stuff (Free), Facebook Local (Free) and Guestboard (Freemium).
Helps groups of people with shared interests plan meetings and form clubs in local communities around the world. Joining an existing meetup is free. However each meetup group can charge dues. The mobile applications are free.