oj! Algorithms - Open Source Java library for mathematics, linear algebra and optimisation. Pure Java, zero dependencies: fast matrices plus LP, QP and MIP solvers.
PHP arrays whose fields HTML-encode themselves when echoed, with chainable methods for filtering, sorting, and grouping database rows. XSS-safe by default, with SmartString's encoder behind it: at least 2.5x faster than calling htmlspecialchars() yourself.
Visit a method over the items in an object, or map visit over the objects in an array. This is an alternative approach to using extend or merge, useful when events are emitted on a method like get or set.