Lambda (formerly FiftyOne) is a modern, high-definition theme for StepMania 5.x. It is designed to serve as the default theme for StepMania 5.1; it features a clean aesthetic with bold colors that reflects modern design trends, yet still maintains a suitable level of energy for a rhythm game. Under the hood, it's also a bit more future-proof than the previous theme, with certain screens featuring more prominent use of backend Lua code to replace legacy methods of rendering particular elements.

Inkscape SVG source code is available for the majority of graphics created in the _src folder on the repository used to develop it, located at https://github.com/ListenerJubatus/smtheme-fiftyOne Some of the original mockups are also included for reference, although they are meant primarily for reference purposes due to changes in the theme's style since these mockups (such as the removal of rounded corners and increased use of chamfered edges and diamond motifs).

The main fonts are the current version of Roboto and Noto Sans https://www.google.com/design/spec/resources/roboto-noto-fonts.html, and Open Sans (although, preferably, Noto Sans should eventually be used in any location Open Sans is currently used). Certain accents make use of the fonts Overpass http://overpassfont.org/ and Zeroes http://www.dafont.com/zero-threes.font

As it incorporates existing code from StepMania, and is intended to possibly be part of the main distribution, Lambda is licensed under the terms of the MIT License.