BuiltWith - Find out the technology behind websites
Mochi - Write notes and flashcards with Markdown and study them with spaced repetition.
Lead Forensics - B2B website analytics and lead generation.
Gainful.io - Capture B2B leads on AngelList, CrunchBase and LinkedIn
FindThatLead Prospector - Feed your sales team with daily leads.
Zorbi - Spaced-Repetition Flashcards - Other tools are built by boomers, Zorbi is built by students.