There is, of course, the LAMP and WAMP toolsets -
if you want to play with WAMP I suggest
www.foxserve.net
- those distros are solid.

as to popularity ? bill-able-time-ity ?
there are more LAMP websites than ASP, any version you want to swing a stick at, at least from the surveys conducted by IDG and InfoWorld and ZD.

So to say "I don't have work in PHP" - then change your customer demographic a bit and you'll find plenty-o-work.

One cool thing to muck about with is XRMS - see http://xrms.sourceforge.net

its a CRM / SFA package thats been getting some press lately .
You can run it on LAMP or WAMP boxes, and of course, if you want to change the data store to VFP - you can, utilizing the adodb package that comes with XRMS . [not a trivial hack, but i've got it to work ] .

Some people like to take a working system and study the code and see whats under the hood. IMO, xrms is great for that .

enjoy your time !! mondo regards [Bill]
[WAMP = Windows/Apache/mySql/php]
[LAMP = linux/apache/mySql/php]