aria2 is a utility for downloading files. The supported protocols are HTTP(S), FTP, BitTorrent, and Metalink. It has a powerful segmented downloading ability, downloading a file from multiple sources and multiple protocols and utilizing your download bandwidth to the maximum. It supports downloading a file from HTTP(S)/FTP and BitTorrent at the same time, while the data downloaded from HTTP(S)/FTP is uploaded to the BitTorrent swarm. Using Metalink's chunk checksums, aria2 automatically validates chunks of data while downloading a file like BitTorrent.
Wslay is a WebSocket library written in C. It implements the protocol version 13 described in RFC 6455. This library offers 2 levels of API: an event-based API and a frame-based low-level API. For the event-based API, it is suitable for non-blocking reactor pattern style. You can set callbacks in various events. For the frame-based API, you can send WebSocket frame directly. Wslay only supports the data transfer part of the WebSocket protocol and does not perform the opening handshake in HTTP. It does not perform any I/O operations for its own. Instead, it offers callbacks for them. This makes Wslay independent of any I/O frameworks, SSL, sockets, etc. It is portable across various platforms, and the application authors can choose I/O frameworks freely.
spdylay is an experimental implementation of Google's SPDY protocol in C. It provides a SPDY framing layer implementation. It does not perform any I/O operations. When the library needs them, it calls the callback functions provided by the application. It also does not include any event polling mechanism, so the application can freely choose the way of handling events. This library code does not depend on any particular SSL library (except for example programs that depend on OpenSSL 1.0.1 or later).