While alternativeto.net doesn't only focus on open source it does offer more regular updates and a wider variety of options.
From the website:
We have one mission: helping you find the right software for your computer or mobile phone. To do this we wanted to rethink the whole process of searching for apps. No more browsing through categories with long lists of crappy software.
Based on our users recommendations we list great alternatives to the applications you want to replace. By joining the site you can participate in the process of making these recommendations better, so please join in!