Some tools I have mentioned in class:
Unpaywall: a browser extension that will find open access version of articles. Useful when you want to find articles that anyone can access.
Hashtagify: a website that has a free tool to find related hashtags and the most popular spelling variant of a hashtag
Bit.ly; tiny.cc; tinyurl.com: 3 tools to shorten links (Twitter does this automatically but not the other social media). tiny.cc will also allow you to create custom links