Klangmeister is described as 'live coding environment for the browser. It lets you design synthesisers and compose music using computer code - without having to install anything on your own computer' and is an app in the Audio & Music category. There are more than 10 alternatives to Klangmeister for a variety of platforms, including Windows, Online / Web-based, Self-Hosted solutions, Mac and Linux. The best alternative is SuperCollider, which is both free and Open Source. Other great apps like Klangmeister are Sonic Pi (Free, Open Source), ChucK (Free, Open Source), Synthesine (Free, Open Source) and Faust (Free, Open Source).
AudioMasher is a live, in-browser audio and music programming environment. The app is based on the Sporth audio programming language by Paul Batchelor, is open-source and can be used online or via self-hosting.
The SOUL platform is a language and an API. The language is a small, carefully crafted DSL for writing the real-time parts of an audio algorithm. The API is designed to deploy that SOUL code to heterogeneous CPUs and DSPs, both locally and remotely.