Wolfram Research announced today that it will make the Wolfram Engine available for free to anyone working on software development projects. You can download it for use in non-production environments here.
The Free Wolfram Engine for Developers will allow developers to implement the Wolfram Language in any standard software engineering stack. (The Wolfram Language, available in a sandbox here, is the multi-paradigm computational language behind Wolfram's best-known products, Mathematica and Wolfram Alpha.) The free engine also has full access to the Wolfram Knowledgebase and its curated, pre-trained neural networks, although you'll need to sign up for a free subscription to the Wolfram Cloud.