Search: DDG is the obvious answer. But also reducing usage of general search is a major life improvement. Wikipedia and Stack Overflow have reasonable built-in searches, as do most sites I view as reasonable sources of information. Most discoverability comes from feeds (blogs, HN, Reddit)--searching limits you to terms you've already thought of. General search seems to lead either to the places already mentioned in good cases, and to low-quality results that waste time and mislead you in bad cases. You can save time and improve thought process by going more directly to sources.

Email: Fastmail. But again, just using email less is helpful. My most common form of communication is using text messages to set up meeting in person.

Facebook: Does this even need a replacement? I haven't made any intentional effort to replace Facebook since I stopped using it, and don't feel any sense of loss. The same goes for Twitter/Instagram. The only thing these services ever did for me was make me feel angry, lonely, or inadequate.

Random side note: Stack Overflow has a serious content quality and up-to-date-ness issue. An alternative is using documentation, reading code, and mastering debuggers/REPLs. This gives you a much better understanding of your tools, and gives you much better solutions as a result.