Yaws is a WWW technology with capabilities similar to the combination of Apache with PHP and a database. Yaws runs faster, with smaller footprint, higher scalability, and higher reliability. Subjectively speaking, it uses a more beautiful technique to generate dynamic pages than other similar technologies.
Tsung is a distributed load testing tool. It is protocol-independent and can currently be used to stress HTTP, WebDAV, PostgreSQL, MySQL, LDAP, AMQP, and XMPP/Jabber servers. It simulates user behavior using an XML description file, reports many measurements in real time (statistics can be customized with transactions, and graphics generated using gnuplot). For HTTP, it supports 1.0 and 1.1, has a proxy mode to record sessions, supports GET, POST, PUT, and DELETE methods, cookies, and basic/digest authentication. It also has support for SSL, WebSocket, and BOSH.
teeterl is a lean, portable implementation of Erlang. teeterl starts from a single executable file without any additional harness. teeterl is built using Apache Portable Runtime, a library tested on dozens of OSes and their flavors. teeterl borrows from industry-standard Erlang/OTP, especially when it comes to compiler front-end. teeterl provides the concurrency power of Erlang without any telecom cruft.
epers stands for "Erlang persistence". As the name suggests, it tries to make it easy to use databases in Erlang programs, to make the language a little more agile, and (humbly) offer a nice adapter for several databases, hiding their implementation details (and the API of the library/framework/driver used to communicate with them). To achieve this, it aims to offer a somewhat consistent API to define and work with your model, while at the same not coupling your code too tightly to it.