Hunter TechLookup - Create lists of websites by technology for free
Checkly - Fresh API monitoring and Site Transaction Monitoring. From one great dashboard.
Setalist - The easiest way to make awesome lists for the internet
Listy Beta - The things you love, privately saved and beautifully listed
Techmap.io - Techmap is a workplace search engine to find companies using technologies (e.g., Rails, PHP, Java, etc.) that are used internally. Finally, a "Google for Workplaces" that helps people find a place to work with technologies they love!
Checklist Generator - Create checklists for free and host them wherever you want.