Vega Visualization Grammar is described as 'Vega is a visualization grammar, a declarative format for creating, saving, and sharing interactive visualization designs'. There are three alternatives to Vega Visualization Grammar for Online / Web-based and Self-Hosted solutions. The best alternative is D3.js, which is both free and Open Source. Other great apps like Vega Visualization Grammar are Vega-Lite (Free, Open Source) and picasso.js (Free, Open Source).
D3 allows you to bind arbitrary data to a Document Object Model (DOM), and then apply data-driven transformations to the document. For example, you can use D3 to generate an HTML table from an array of numbers.
Vega-Lite provides a higher-level grammar for visual analysis, comparable to ggplot or Tableau, that generates complete Vega specifications. Vega-Lite specifications consist of simple mappings of variables in a data set to visual encoding channels such as x, y, color, and size.