Discontinued
The project is no longer updated. Last version, 0.9, released in September 2010, can be still downloaded from the official website.
Linux port of the Mac OS X application 
SelfControl . Uses Perl/Gtk2 + iptables. Provides basic timed blocking of specified hosts.
SelfControl . Uses Perl/Gtk2 + iptables. Provides basic timed blocking of specified hosts.Recent user activities on SelfControl -- The Linux port
- JonesCutemba added SelfControl -- The Linux port as alternative(s) to iChooseTo
- hadi4172 added SelfControl -- The Linux port as alternative(s) to Time Companion
- braky added SelfControl -- The Linux port as alternative(s) to Digital Wellbeing
It's good on my Ubuntu 12.10. It blocks out all distracting web sites. You can decide for how long you want to block those sites and once started, you cannot unblock them, you just have to wait for it to expire. There's a bug regarding the block list (before starting it) because it's so small you can't select one of the entries and delete it (say, you have a duplicate for a website and you want to eliminate one of the entries). However there is a work-around -- in sudo mode, just copy/paste a piece of code in the UI.pm file under /usr/share/perl5/SelfControl/, instruction are given in their GIThub section (google it, if you're having trouble). It worked for me: I was able to delete one of the entries for youtube.com!