Acunetix Vulnerability Scanner - Acunetix Vulnerability Scanner is a platform that offers a web vulnerability scanner and provides security testing to users for their web applications.
F-Droid - F-Droid is an interesting alternative for Android users who want to try something different and not have to use the Goole Play store all the time.
Nessus - Nessus Professional is a security platform designed for businesses who want to protect the security of themselves, their clients, and their customers.
APK Pure - Download apk for Android with APKPure APK downloader. NoAds, Faster apk downloads and apk file update speed. Best of all, it's free
StackPath - Secure Content Delivery Network, DDoS, WAF Service
APKMirror - Android Market and APK Downloads