HostingChecker, Varna, Bulgaria
At HostingChecker we have free tools for developers and sysadmins that we constantly develop. Our main tool displays data on who is hosting a website, what is the IP, ASIN, where is the domain hosted and reverse DNS. We also have reverse IP lookup tool that can get information on how many domains are hosted behind a single IP address and can identify the neighboring domains. Currently we have 4 Dell r720 servers that have about 12 virtual servers each.
We use them for the tools and scraping and analyzing the data. We also have a web server with Nginx as reverse proxy for Apache. We also use Debian as a base on our site speed tool that we use when making the reviews for our UK project https://top5hositng.uk. This tool continuously monitor the demo web sites on different web hosts for their web performance (the tech stack is the Coach, Browsertime, PageXray and Graphana).
We chose Debian over other Linux distributions because of its long life cycle, stability, low resource footprint, great community and package manager. Debian is making the work of the sysadmin much easier.