eXist-db vs PouchDB

eXist-db is a free, open-source NoSQL document database and application platform centered on XML. Its native engine stores textual or binary documents without requiring a database schema, and it is designed for self-hosted deployment on Linux, macOS, or Windows. The product implements XQuery 3.1, though some features and functions are unsupported, and RESTXQ lets developers deploy RESTful services from XQuery annotations. Its interfaces include REST-style HTTP, SOAP, XML-RPC, and WebDAV. A browser-based IDE provides syntax coloring, code completion, and error checking for application artifacts. Full-text search uses an implementation-specific Apache Lucene approach rather than the W3C XQuery and XPath Full Text 3.0 specification. Security extends Unix permissions with access control lists and external authentication realms. The software is licensed under the LGPL for academic, non-commercial, and commercial use. The documentation lists Java 8 for versions 3.x–6.x or Java 21 for version 7.x, about 500 MB of disk space, and at least 512 MB of memory.

PouchDB is a free, open-source JavaScript database for storing application data locally and synchronizing it with CouchDB and compatible servers. It keeps data available offline and can sync local and remote databases after a connection returns. Its replication API can follow later changes and retry after connection failures when configured. PouchDB runs in browsers and Node.js, as well as Cordova, PhoneGap, NW.js, Electron, and Chrome apps. Browser storage defaults to IndexedDB, while Node.js defaults to LevelDB. Documents can include image or audio attachments stored as base64 data or Blobs. PouchDB includes a map/reduce API; Mango queries require the separate pouchdb-find plugin. Its asynchronous API supports callbacks, promises, and async functions, and the project names Angular, React, Ember, and Backbone as framework examples. Listed compatible servers include CouchDB 1.x, 2.x, and 3.x, Cloudant, and PouchDB Server. Replication requires a backend that speaks the CouchDB replication protocol. The project homepage says Apache PouchDB is undergoing incubation at the Apache Software Foundation.