libraries.io — Search and dependency update notifications for 32 different package managers, free for open source
Namae - Search various websites like GitHub, Gitlab, Heroku, Netlify, and many more for the availability of your project name.
searchcode.com — Comprehensive text-based code search, free for Open Source
tickgit.com — Surfaces TODO comments (and other markers) to identify areas of code worth returning to for improvement.
CodeKeep - Google Keep for Code Snippets. Organize, Discover, and share code snippets, featuring a powerful code screenshot tool with preset templates and a linking feature.