Sitecore 9 new features

• Sitecore 9 is a major new release with new features and brand new framework.
• Sitecore requirement: Win Server 2016/ 12 R2 / Win 10 /8.1 IIS 8.5 / 10 .Net Framework 4.5 + SQL server 2016 / 2014 SP2 for XM or CMS mode. Mongo DB  + Cosmos DB (future release)
• Solr 6.6 and Azure Search
• Silverlight is not supported
• Sitecore 9 is secure out of the Box (HTTP's enabled)
• Sitecore Installation framework (SIF) for sitecore installation. 
• SIM is not supported in Sitecore 9.
• Solr or Azure Search support (for xConnect)
• Search API feature ( Highlight, Spellcheck, Suggest etc)
• Config Load Order – Customize your order of loading component.
• New Rule-based configuration 
• Support for Federated Authentication (FB, Google, MS, OpenID, AzureAD, Twitter, SAML custom Auth.
• Support for Custom Roles
• Dynamic Placeholders (most wanted feature)
• xConnect - is the service layer that sits in between the xDB and any trusted client, device, or interface Ref: https://doc.sitecore.net/developers/xp/xconnect/xconnect-overview/index.html
• WFFM is dead (but will be supported till Sitecore 9)
• Newly designed web forms, scalable e-mail marketing, and rich automation for marketers
• New Marketing Automation UI / Dashboard
• Speak 3 is based on Angular JS.
• Support for Live Events
• JavaScript Service (JSS) is a newly introduced feature– Powerful headless capabilities for front-end developer, personalization. 
• JSS is based on JS/ NodeJS/ Json, Custom JS Controller.
• JSS feature is under Tech Preview.
• New Experience editor.
• Support for device detection
• New documentation site–
• https://doc.sitecore.net/developers/ 
• https://jss.sitecore.net/
• http://helix.sitecore.net/
• Future release – Sitecore Cortex / Zenith / Commerce 9 / SXA Storefront
• Sitecore 6 & 7 Support is Discontinued.

I have summarized one-pager details of new Sitecore 9 features. Hope this might be helpful. Please feel free to provide your feedback/comments.