The dyncall library project provides a clean and portable C interface to dynamically issue foreign function calls using small call kernels written in assembly. Instead of providing code for every bridged function call, which unnecessarily results in code bloat, only a modest number of instructions are used to invoke all calls.
LibU is a multiplatform C library that comes under a BSD-style license. It includes many interdependent modules for accomplishing several tasks: memory allocation, networking and URI parsing, string manipulation, debugging, and logging in a very compact way, plus many other miscellaneous tasks. It has a small footprint (about 70KB for the default configuration), it is modular, and it has a multiplatform nature, making it an ideal candidate for embedded systems. KLone is an example of such usage.