Vespa is described as 'engine for low-latency computation over large data sets. It stores and indexes your data such that queries, selection and processing over the data can be performed at serving time' and is an app in the Development category. There are eight alternatives to Vespa for a variety of platforms, including Self-Hosted solutions, Windows, Linux, Online / Web-based and SaaS. The best alternative is elasticsearch, which is both free and Open Source. Other great apps like Vespa are Algolia (Free Personal), Apache Solr (Free, Open Source), wordpress i-search pro (Paid) and Apisearch (Freemium, Open Source).
Solr is an open source enterprise search server based on Lucene search library, with XML/HTTP and JSON APIs. Its major features include powerful full-text search, hit highlighting, faceted search, dynamic clustering, database integration, and rich document handling.
ZIR AI allows application developers to add sophisticated ML-powered text search to their applications and platforms. It provides high performance gRPC APIs for indexing and running queries, encryption in transit and rest, and an OAuth 2.0 security model.
Appbase.io provides a supercharged Elasticsearch experience with a #nocode relevance control plane (or JS UI components or a declarative REST API) and out-of-the-box search/click analytics and insights.