With RISC OS switching to the Apache licence, here is your brief intro to the world of Apache....
Apache the software program
Apache is a key building block of the Internet. It runs on many of the servers which make up the Internet and allows them to provide the websites you use every day. Its many features include the ability to host multiple websites on a sever, control access and provide security, execute scripts and commands when you access pages, log website activity, and a whole host of other features. You use Apache every day without realising it.
Apache the licence
All software has a licence which defines what rights you have and what use you can make of a piece of software. For example, most commercial software bans you from trying to dissect it and give it away to your friends.
The Apache licence is one of several Open Source licences. These generally come with free software (as in you do not have to pay for it) which includes the source code. The big difference in Open Source licences is that some are viral (with the GPL you have to release any software which uses it under the same licence so it 'infects' the software) and non-viral (you can use it with other software including commercial software so long as you respect the rules on the original software).
It is possible to release software under more than one licence. A nice example is the PDF library Itext, which you can use for free under the AGPL licence (requiring you to release your code for free as well with the source code), or buy a commercial version (identical except it comes with a commercial licence removing this requirement so you can use in commercial software).
If your aim is to encourage maximum update and usage, you would choose a non-viral licence such as the Apache licence which is what RISC OS now uses.
If you own the software, you can choose to change the licence (as RISC OS Developments has done having acquired RISC OS), but you cannot modify the licence on software belonging to someone else).
Apache the foundation
There is also an organisation called the Apache Software foundation which provides a home for a large number of software programs developed under the Apache licence. Most of these are technical and you might have heard of them if you are a software developer (ie Ant, Groovy, Hadoop, Maven, Perl) or runs on servers providing Internet services (ie SpamAssassin, Tomcat).
Apache is an organisation of individuals (no Company/Corporate membership option) and anyone can join. It also organises conferences and promotes software development.
Anyone can use the Apache licence in the software. This is perfectly acceptable and many other software projects have been doing the same for many years.
If you want your software to be an 'official' Apache project, you also need to follow the apache rules on how software is developed. This lays down a clear methodology and governance.
Many of the software projects which are Apache projects started life outside Apache and have joined by adopting the Apache rules. For the last 2 years, the Java IDE NetBeans has been transitioning to an Apache project (I have had a minor involvement in that giving me a very interesting viewpoint of the Apache foundation).
More details on Open Source licences at GNU website