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Agreed, Redis is truly wonderful, I've used it extensively as both a cache lookalike and also as primary datasource (as long as your data size/growth is known and manageable on RAM, which is pretty common for many projects and current hosts) and it's always super fast, reliable and easy to work with.

Redis + nginx (openresty).

Lua in both places. So (ab)useful!

Not tested recently, but 3 years ago it was said that Redis was slightly faster than memcached for PHP sessions -for example- and I benchmarked it to decide to change. Add persistence to that formula and Redis was a winner for me (put your app into maintenance mode, reboot server(s), enable app again and your users can just resume operations...)