In the 'early days' most software had to be 'sourced' from different locations. The only big source of software in one place was Hensa on the University systems if you were lucky enough to have access. You could also connect to Bulletin boards (Arcade BBS) or get floppy disks through the post from Skyfall or APDL).
You can still hunt around (and there are lots of sites with gems we will be looking at in 2017 on IconBar), but in 2017 you have really easy access to huge sources of software straight from your RISC OS desktop. All you need is TWO programs.
PlingStore ( ie !Store) gives you access to a range or both free and commercial software (which you can buy with a credit card via the software). All software includes details of the software, website links, screenshots and you can search and explore the software on offer. You will find lots of favourites from David Pilling, R-Comp, Steve Fryatt, Chris Johnson, Sine Nomine and many others.
PlingStore tracks which versions of the software you have downloaded so it can also offer you the option to get free updates or buy commercial ones. If you are using R-Comp software, they provide a service to update the store with your current purchases to you can use it for updates when they release new versions.
When PlingStore runs, it checks on the Internet to update its information, so it can tell you about new software, updates or special offers.
!PackMan has developed out of RiscPkg. This brought dependency manangement based on Linux solutions to RISC OS (software can now describe what other software it works with and what it needs).
Dependency management is a big problem on many platforms (and trying to fix it on the Java platform has been the big issue for the last 2 releases of Java). Simply, the problem is that you download a new piece of software which needs version 4 of another library. So you install that on your machines. You then find that all your other software stops working as it only runs on version 3.... RedHat came up with a good solution to this problem which RiscPkg uses.
!PackMan builds ontop of this with a slick front end. It also includes a list of software and it knows what other software (dependencies) this software has. So it can ensure you have the software or download it for you as well. As with PlingStore it gives you a wide range of software and it can update its details with new releases when you run it. There is no payment options in !PackMan so all the software is free. !PackMan has some nice features to not only install the software, but add to Apps, run on startup, etc.
Both applications need some discipline to get the most from them. They do not look at your system and spot existing software, and PackMan has a standard location for all software. So you may be better off deleting existing software, and downloading a new copy in the new location through the package manager.
I am also pleased to say that there is little overlap and duplication between the software both offer. In general (apologies for slight over-simplification) PlingStore offers both 'original' commercial and free software from well-known RISC OS companies and developers while PackMan gives you access to the conversions to RISC OS platform from riscos.info and other sites (fonts, !Otter, games, tools, etc) which has grown from Peter Naulls' original Unix Porting Project.
Both applications are free and should be on your machine!