NanoHttpd is a lightweight HTTP server designed for embedding in other applications. It's only one Java file, in two "flavors", one strictly Java 1.1 compatible, and one at "current" standards. It supports GET, POST, PUT, HEAD and DELETE requests, and supports file uploading with very small memory overhead. Temp file usage and the threading model are easily customized.
fio is an I/O tool meant to be used both for benchmark and stress/hardware verification. It has support for 19 different types of I/O engines (sync, mmap, libaio, posixaio, SG v3, splice, null, network, syslet, guasi, solarisaio, and more), I/O priorities (for newer Linux kernels), rate I/O, forked or threaded jobs, and much more. It can work on block devices as well as files. fio accepts job descriptions in a simple-to-understand text format. Several example job files are included. fio displays all sorts of I/O performance information, including complete IO latencies and percentiles. Fio is in wide use in many places, for both benchmarking, QA, and verification purposes. It supports Linux, FreeBSD, NetBSD, OpenBSD, OS X, OpenSolaris, AIX, HP-UX, Android, and Windows.
The CyaSSL embedded SSL library is a lightweight SSL library written in ANSI C and targeted for embedded and RTOS environments, primarily because of its small size, speed, and feature set. It is commonly used in standard operating environments and cloud services as well because of its royalty-free pricing and excellent cross platform support. CyaSSL supports industry standards up to the current TLS 1.2 and DTLS 1.2 levels, is up to 20 times smaller than OpenSSL, and offers progressive ciphers such as HC-128, RABBIT, and NTRU.
Yate is a next-generation telephony engine. While currently focused on Voice over Internet Protocol (VoIP) and PSTN, its power lies in its ability to be easily extended. It supports SIP, H.323, IAX, MGCP, Jingle, Jabber, E1, T1, analogic, robbed bit, ISDN PRI, BRI, and SS7. YateClient is an Instant Messenger and Voice application for Jabber/Jingle IM, SIP, H.323, and IAX VoIP protocols.
MundoCore is a lightweight and easy-to-use communication middleware to integrate heterogeneous software systems, consisting of services written in different programming languages and running on different operating systems. It also offers specific support for mobile and ubiquitous computing environments.
libre is a generic library for real-time communications with asynchronous I/O support. It is written in portable POSIX source code that conforms to the ANSI C89 and ISO C99 standards. It is robust and fast, with a low memory footprint. It also features RFC compliance and support for IPv4 and IPv6. Protocol implementations include SIP, SDP, RTP/RTCP, BFCP, DNS, STUN/TURN/ICE, HTTP, and WebSockets.