Redis

Redis is the wildly popular open-source, in-memory data store used as a database, cache, and message broker. By keeping data in memory, Redis delivers sub-millisecond performance, making it the default choice for caching, session storage, rate limiting, leaderboards, queues, pub/sub messaging, and other real-time use cases. It supports rich data structures (strings, hashes, lists, sets, sorted sets, streams) and has grown into a multi-model platform with modules for JSON, search, time series, probabilistic data, and — increasingly important — vector search for AI applications.

Developers use Redis to make applications fast and scalable. As a cache in front of a slower database, it dramatically reduces latency and load; as a real-time data layer, it powers features like live counters, queues, and messaging; and Redis vector search and semantic caching support AI/LLM apps (RAG, embeddings). Redis is available as free open-source software you self-host, and as Redis Cloud — a fully managed service on AWS, GCP, and Azure with high availability, clustering, and Active-Active geo-distribution — plus Redis Enterprise for self-managed deployments at scale.

Redis serves developers and companies of all sizes needing fast, real-time data. The open-source software is free to self-host; Redis Cloud offers a Free tier (30 MB), Essentials plans from about $5/month (scaling by memory/throughput, up to a few hundred dollars), a Pro tier from about $200/month on dedicated infrastructure (production workloads commonly $1,500–$6,000+/month), and custom Enterprise. It competes with Memcached, Amazon ElastiCache, MongoDB, and Hazelcast, differentiating on speed, versatility, and its vast ecosystem.