Twidere - Tired of seeing ads and promotions in your timeline, being disrupted by tweets from bots and people...
BuiltWith - Find out the technology behind websites
Pawoo - Japanese Mastodon client with English translation.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
AndStatus - A client for Twitter, Mastodon, GNU Social and Pump.io
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.