Rosetta Code is a programming chrestomathy site. It presents solutions to the same task in many different languages, to demonstrate how languages are similar and different.
Ada Style Guides
Ada Style Guide By a bunch of top contributors [2017-2021] (CC-BY-SA)
Ada 95 Style Guide DoD - Ada Joint Program Office Software Productivity Consortium [1995] (CC-0)
On-line Learning Materials
Presentation of the Ada Programming Language
Ada Programming tutorial from AdaCore
An Introduction to Ada by Jim Rogers (Ada Resource Association)
Ada and SPARK on ARM Cortex-M by Maciej Sobczak Inspirel [2017]
The Big Online Book of Linux Ada Programming by Ken O. Burtch PegaSoft Linux Association [2009]
Ada Programming tutorial by a bunch of top contributors (CC-BY-SA)
Why Ada ? ada-lang.io
Programming with Ada by Paul Y. Jarrett
Ada 95 tutorial by Gordon Dodrill Coronado Enterprises [1998]
Ada 95: The Craft of Object-Oriented Programming by John English originally published by Prentice Hall [1996] (CC-BY-SA)
On-line / interactive Ada compiler
(free) e-Books ~ PDF
Ada for the Embedded C Developer by Quentin Ochem, Robert Tice, Gustavo A. Hoffmann, Patrick Rogers AdaCore [2021]
Ada for the C++ or Java Developer by Quentin Ochem AdaCore [2021]
18 free e-Books available from AdaCore
Ada - a crash course, with sources by Peter C. Chapin GitHub [2020] CC-BY-SA
Ada Distilled by Richard Riehle AdaWorks [2011] CC-BY-SA
Ada-95: A guide for C and C++ programmers by Simon Johnston ICL Retail Systems [1995]
Books
Programming in Ada 2012, with a Preview of Ada 2022 by John Barnes Cambridge University Press [2022]
Beginning Ada Programming: From Novice to Professional by Andrew T. Shvets Apress [2019]
Analysable Real-Time Systems: Programmed in Ada by Alan Burns,Prof Andy Wellings CreateSpace Independent Publishing Platform [2016]
Building High Integrity Applications with SPARK by John McCormick, Peter Chapin Cambridge University Press [2015]
Building Parallel, Embedded, and Real-Time Applications with Ada by John W. McCormick, Frank Singhoff, Jérôme Hugues Cambridge University Press [2011]
Real-Time Systems and Programming Languages: Ada, Real-Time Java and C/Real-Time POSIX by Alan Burns, Andy Wellings Pearson Education Canada [2009]
Ada for Software Engineers by Mordechai Ben-Ari Springer [2009]
Ada 2005 Rationale: The Language, The Standard Libraries by John Barnes Springer [2008]
Concurrent and Real-Time Programming in Ada by Alan Burns, Andy Wellings Cambridge University Press [2007]
Ada Plus Data Structures: An Object Oriented Approach by Nell B. Dale, John W. McCormick Jones & Bartlett Learning [2006]
Software Engineering With Ada by Grady Booch, Doug Bryan, Charles G. Petersen Addison-Wesley Professional [1993]
Comprehensive Bibliography referenced by the«Ada Resource Association»