What are the basics of SAP NetWeaver in a nutshell?

What is the basic purpose of ALE, IDoc & NetWeaver technologies? Where it can they be used? Can I get some basic information?

In a nutshell, NetWeaver is the common brand name for all the SAP products that follow the SAP R/3 ERP software. NetWeaver delivers two completely independent (and incompatible) development frameworks. The SAP ABAP engine and the SAP WebDynpro J2EE engine. Most current SAP products are mostly written in ABAP, while Java applications on the J2EE engine gain some popularity.

IDoc is the data format used to exchange data with SAP systems. ALE is called a suite of tools used to control and monitor the flow of IDocs in and out the SAP systems.

I recommend to read the great SAP Netweaver for Dummies book. The book is based on the curriculum of the basic SAPTEC course of the SAP academy and gives a very good overview how the NetWeaver landscape is built and how it evolved from the celebrated SAP R/3.