Product documentation links
SQL Server product documentation (with links back to SQL Server 2005)
(always look for the “What’s New” section when a new version arrives)
Transact-SQL Reference (Database Engine)
Features Supported by the Editions of SQL Server
Hardware and Software Requirements for Installing SQL Server
Power BI product documentation
See also: Microsoft SQL Server Version List
(“Lists all of the know Service Packs, Cumulative Updates, Patches, Hotfixes, and
other builds of SQL Server back to SQL Server 6.0)
Power BI download links 
Power BI Desktop (updates released almost monthly)
Power BI Report Server (updates released about every 3-4 months)
Power BI Gateway Standard Mode | Personal Mode
SQL Server and related download links 
(including Reporting Services / SSRS)
SQL Server 2022 Developer Edition download (and Express Edition) 
SQL Server Management Studio download, currently 20.1. Make sure you read the Release Notes.
You may choose to install or stay with 19.3 (OK, 19.3.4.0 released January 10, 2024) or one of the other previous releases. For some time now Azure Data Studio is now automatically installed alongside.
Microsoft® SQL Server® 2017 Feature Pack
SQL Server Mobile Report Publisher download (going away)
AdventureWorks sample databases (this page has links to both .bak files and script files, and, OLTP and DW versions of Adventureworks, and multiple versions as well!)
Wide World Importers sample database v1.0
Microsoft Contoso BI Demo Dataset for Retail Industry
(published 2010, .bak and .abf files; lots of rows too)
A fictitious retail demo dataset used for presenting Microsoft Business Intelligence products.
See also Jeremy Kadlec’s “SQL Server Download Quick Links” found at MSSQLTips
Other download links
Visual Studio downloads and homepage
What about SQL Server Data Tools (SSDT) for Visual Studio?
Azure Feature Pack for Integration Services (SSIS)
Adventureworks sample databases (GitHub)
WideWorldImporters sample databases (quite a number of resources, on GitHub)