mpmath is a free (BSD licensed) Python library for real and complex floating-point arithmetic with arbitrary precision. It has been developed by Fredrik Johansson since 2007, with help from many contributors.

Need to encode, transmit, or store encrypted or signed data? saltpack is a streamlined, modern solution, designed with simplicity in mind. It is easy to implement & integrate. We've made few crypto decisions and instead leave almost all of the heavy lifting to the NaCl library.

saltpack is a binary message format, encoded using the MessagePack format. Messages are broken up into reasonable (1MB) chunks, over which regular NaCl operations are performed. We have taken pains to address many of the shortcomings of current message formats: (1) only authenticated data is output; (2) repudiable authentication is used wherever possible; (3) chunks cannot be reordered or combined with other transmissions; (4) the public keys of senders and recipients can be hidden; and (5) message truncation is detectable.

Implementations in Go and Python are available at https://saltpack.org/implementations  The format is used by https://keybase.io/

For a long time, we were unhappy with having to care about security issues and Linux distribution maintenance on our various Raspberry Pis.
Then, we had a crazy idea: what if we got rid of memory-unsafe languages and all software we don’t strictly need?
Turns out this is feasible. gokrazy is the result.

NomadBSD is a persistent live system for USB flash drives, based on FreeBSD®. Together with automatic hardware detection and setup, it is configured to be used as a desktop system that works out of the box, but can also be used for data recovery, for educational purposes, or to test FreeBSD®'s hardware compatibility.

LambdaNative is an open-source (BSD licensed) cross-platform development environment written in Scheme (Gambit-C), supporting Android, iOS, BlackBerry 10, OS X, Linux, Windows, OpenBSD, and NetBSD. Some cross-compiler support for Raspberry Pi (Carlson-Minot) and OpenWrt (Sitara) also exists. See also https://www.lambdanative.org/

ISA-L is a collection of optimized low-level functions targeting storage applications. ISA-L includes:
   Erasure codes - Fast block Reed-Solomon type erasure codes for any encode/decode matrix in GF(2^8).
   CRC - Fast implementations of cyclic redundancy check. Six different polynomials supported.
       iscsi32, ieee32, t10dif, ecma64, iso64, jones64.
   Raid - calculate and operate on XOR and P+Q parity found in common RAID implementations.
   Compression - Fast deflate-compatible data compression.
   De-compression - Fast inflate-compatible data compression.
BSD 3-Clause "New" or "Revised" License.
According to https://github.com/catid/cm256, ISA-L uses a O(N^3) Gaussian elimination solver for decoding. The CM256 decoder solves the linear system using a fast O(N^2) LDU-decomposition algorithm from "Pivoting and Backward Stability of Fast Algorithms for Solving Cauchy Linear Equations" (T. Boros, T. Kailath, V. Olshevsky), which was hand-optimized for memory accesses.
See also https://github.com/catid/leopard for a fast O(N log(N)) RS erasure decoder.

TinyScheme is a lightweight Scheme interpreter that implements as large a subset of R5RS as was possible without getting very large and complicated. It is meant to be used as an embedded scripting interpreter for other programs. As such, it does not offer IDEs or extensive toolkits although it does sport a small top-level loop, included conditionally. A lot of functionality in TinyScheme is included conditionally, to allow developers freedom in balancing features and footprint.

Found via a post on the TUHS mailing list
https://minnie.tuhs.org/pipermail/tuhs/2019-September/018465.html

mpsh is an experimental command interpreter for Unix systems written by Dave Fischer at the Center for Computational Aesthetics and distributed under the 3-clause BSD license.

cl-6502 is a Common Lisp emulator, assembler and disassembler for the MOS 6502 processor.