Wouldn't it be great to have a solution for every problem you can find, at your fingertips, and often even freely available? This is a gap that the Open Source Software movement has filled in little over a decade for the mainstream. It's a side effect of the Internet's jump into the lives of people everywhere!
The concepts behind Open Source Software have been around for more than a century. This is sharing technologies and ideas so many can improve them, support them, and use them; Openly. Another great aspect, is the high volume of free open source software out there to choose from!
Where open source software differs so much from conventional commercial software, comes from the source code which can makes it function. It enables anyone to customize or outright change the software as wanted/needed. It leads to many more developers being available to service, train, and customize the software to what you need.
Often, the open source software is very useful right out of the box, with documentation that details it well. This comes from more people being involved in it's design, from different views of it. It definitely brings diversity! Though if there are changes needed to make it look, feel, or function differently, you should have no problem finding someone that can effect the change(s) to it.
We all see the benefits of Open Source Software everyday online. From the technologies we use, that got ideas/functionalities they first saw in some open software release (such as Internet Protocol and web pages/browsing and serving) to full blown office productivity software, such as OpenOffice.org which does nearly everything other word-processing/database/spreadsheet bundled products do.
Whether you are looking to make a website, run a server computer, fill your desktop/laptop with useful software that keeps you productive doing your work, and not simply computing; you will undoubtedly find open source software to do it with. You should have no problem even finding some games too, if you need that sort to relieve stress at times.
As far as the long term picture, seldom does something useful ever die in open source software. If for some reason, a particular offering decides to discontinue, it's highly likely that someone will continue with the source code left in improving it, or making something even better than the original.
If you really like some particular open source project, and the software they provide, you might look to donate some to their efforts, as beyond the time they put in (often for free), there are occasionally expenses involved too. Many do accept small monetary donations, though more often help with feedback is welcomed. From a developers point of view, it can be the difference between continued improvement, and maybe winding up with no time to put into the open source project.
In the end, whatever your need, you can find a open source solution to fill it! You will likely find more than one to choose from, and there are many more to come. And remember, if the open source software you use leaves a few things to desire, you should have no problem finding someone to extend it to accommodate your needs, fairly affordable.