eINIT is an alternative init system. It's quite fast, since it can potentially be used without the help of any scripting at all, but it is still flexible and extremely modular. The focus is on speed and parallelisation, mostly with embedded devices and low-downtime servers in mind, and benchmarks do suggest that it's doing a fairly good job at that. It compiles cleanly (and should thus work, provided someone writes appropriate modules) on Linux, FreeBSD, and Darwin/Mac OS X.
Curie is a very minimalistic, tiny C library. It supports basic I/O, basic networking, S-expression based I/O, signal handling, process handling, and I/O multiplexing. If the target architecture is explicitly supported, statically linked binaries may be as small as 4-20 kilobytes; if not, then it only relies on the host's C library. The library explicitly does not provide a POSIX interface so that it may be used in conjunction with a regular host libc (or without one).
Topologic is a simple renderer for certain higher-dimensional geometric primitives and some regular 3D shapes. The idea is to make it easy for students of certain higher-dimensional maths and physics topics to visualize the typical primitives in those fields and get a grasp for the topic.
markov.sql implements third order (and lower) model Markov Chains, including training and generation, in pure SQL(ite). The source code archive also contains a pre-trained SQL dump with models based on the 1990 US Census Bureau data sets for first and last names, and an excerpt of the 2012 US tax office corporation names.
libefgy is a set of C++ headers containing lots of templates loosely related to maths. The headers include templates for fractional arithmetic, big integers (and thus "big fractions"), calculating ?, e, and some calculations with those (for trigonometrics), matrix manipulations, tuples, polar and Euclidian spaces in arbitrary dimensions, (perspective) projections, colour space manipulations in RGB and HSL, and assorted other things.