botmarker is described as 'bot that helps you bookmark tweets you like'. There are three alternatives to botmarker, not only websites but also apps for iPhone, iPad and Android. The best alternative is Charm: Collect Tweets on Twitter, which is free. Other great sites and apps similar to botmarker are Floatbot (Freemium) and Twitter Bookmarks (Free).
Charm is a Twitter companion app for iOS to organise Tweets into collections, save articles for later, cue up playlists of music you find, or transcribe conversations. You can use it to tell stories, hold on to jokes, capture Tweetstorms and monologues.