I recently published a post in SAPYard about the SAP Debugging course that I created for Academy OnSap. The SAPYard is a great site, full a useful information for SAP consultants and users. I am very grateful for their help spreading the word about the SAP debugging course and I also want to highlight they have great content.
For example, they have a series of tutorials about Web Dynpro, a topic that nowadays is fundamental for programmers. Still on ABAP, you will also find interesting this more advanced post about delete on internal tables. And they also have a lot of content and expertise on SAP HANA (eg, HANA Views).
There are amazing SAP resources outside the walls of the SAP company. Official SAP portals are good and important but in my opinion the quality of the independent community is what makes the SAP ecosystem so great.