A short reasoned selection from my bookmarks

RobTex

DNSLookup, Domain informations,Network informations

https://www.robtex.com/

Shodan

Search engine used to find Internet of Things (IoT) connected devices around the world: reports open port and services.

Web Inspector

Scans URL in real-time

http://app.webinspector.com/online_scan

UrlVoid

Scan websites with multiple website reputation engines to check if the website is safe and legit.

IpVoid

Scans an IP address using multiple DNS-based blacklists to facilitate the detection of IP addresses involved in spamming activities.

VirusTotal

Free service that analyzes suspicious files and URLs and facilitates the quick detection of viruses, worms, trojans, and all kinds of malware.