TagTeam is an RSS / Atom / RDF aggregator with the ability to filter and remix its input feeds with a high degree of flexibility.  Items can be added directly to TagTeam “bookmarking collections” via the provided delicious-like bookmarklet, and these items can be remixed and filtered like any other item.

TagTeam can aggregate content from anything that emits RSS, Atom, or RDF. This includes delicious, zotero, WordPress, twitter, mediawiki, connotea, blogger, github, and too many other applications and services to mention. It uses the feed-abstract gem, written as part of this project to create a better way of dealing with structured feeds. feed-abstract understands some generators and does magical things - like turning twitter hashtags into actual tags on aggregated items.  Has its own search engine.

Written in Ruby on Rails, uses Postgres as its backend.  Redis for queue processing.  The search component is written in Java.

Github: https://github.com/berkmancenter/tagteam/

Commodore BBS telnet listing. Even has an API.

An online server that generates different kinds of random data for testing and development - integers, sequences, phone numbers, credit card numbers, names... you name it, they generate it.  Has a REST API, 1k hits/month, request a free API key.

privacyIDEA is a modular authentication server that can be used to implement 2fa with your existing applications.  Can use many different back-ends, from LDAP to Active Directory to flat files.  Has a self-service portal for users.  Policies enforce different requirements on groups.  Supports HOTP, TOTP, SafeNet, eToken Pass, Safeword, OTP cards, Google Authenticator, RADIUS, SMS one-time tokens...

Has a TokenClass which is designed for adding new authentication devices.  Has a REST API.  Plugins for many services available.  Supports detailed audit logging.  Supports multiple databases for its datastores.  Database contents are AES encrypted.

Github repo: https://github.com/privacyidea/privacyidea

Dendrite will be a Matrix server written in Go.  Requires Kafka (if run as a cluster of microservices) or something called Naffka (an embedded in-process workalike) if run monolithically.  Requires Postgres as its back end.

A module for Prosody that implements a REST API.  Meant for building bots.  Can both accept and transmit XML and JSON.  Can be configured to send replies to a callback URL.  HTTP status codes 202 and 204 are interpreted as "message accepted" without needing to send an XMPP reply stanza.

SeaweedFS is a simple and highly scalable distributed file system. There are two objectives:  to store billions of relatively small files, and to serve those files fast. Implements an object store with O(1) disk seek and an optional filer with a POSIX interface.  Metadata can be stored in one of several RDBMSes.  Speaks HTTP(S).  Supports multiple access APIs, including S3, HDFS, and WebDAV.  Can automatically back itself up offsite.  Supports multiple URI formats, with varying degrees of niceness.  Large files are chunked transparently to the user.

A canonical description of HTTP verbs/methods and how they're used in a RESTful context.  Includes examples of both groups of items and specific items.

An HTTP server that sits between Redis and whatever clients you have and implements a REST API for the Redis protocol.  Can even be used to upload and store files using PUT requests.  Defaults to JSON but can return other data formats by adding an extension (.json, .txt, and so forth).  JSON objects stored are single items.  Also implements pubsub and WebSockets.  Implemented in C.

Github: https://github.com/nicolasff/webdis

An easy to use Python framework for developing webapps.  Supports static pages as well as Jinja2 templates automatically.  Supports asynchronous operation.  Like Requests, tries to be easy to use and somewhat intuitive.  You can select the data type you send back, from plain Unicode text to YAML.