Math Doubts is an online mathematics education service, where students learn mathematics from basic to advanced level, teachers improve their teaching skill and mathematicians share researching projects with the mathematics fans.
Algolia - Algolia's Search API makes it easy to deliver a great search experience in your apps & websites. Algolia Search provides hosted full-text, numerical, faceted and geolocalized search.
Teachoo - Learn Maths, English, Science free at Teachoo
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Khan Academy - Khan Academy offers online tools to help students learn about a variety of important school subjects. Tools include videos, practice exercises, and materials for instructors. Read more about Khan Academy.
Site Search 360 - Site Search 360 enhances and improves your built-in CMS or product search with autocompletion, semantic search, filters, facets, detailed analytics, and a whole lot of customization options.
Udemy - Online Courses - Learn Anything, On Your Schedule