Java
It seems that Java was open today. I can't help thinking that Sun was nudged by gcj. I run gcj web plugin in Firefox to access Bladecenter, and gcj proper to build and run small Java toys (like USBMon). I also tinkered with running Azureus and RSSOwl, and although they aren't mainstay applications for me, they are not little toys, and they work with gcj and Classpath. So, Sun opened Java when it became patently obvious that Classpath is on the course to obsolete Sun's implementation.
Regardless of the reasons, I think that open Java is great news. I loved hacking in Java. The language was great. Libraries were... hard to evaluate for a drive-by programmer like myself, but I saw them getting better quite a bit (especially when you count non-Sun things like SWT, RxTx, etc.).
I never was big on WORA (actually, considered it a marketing fraud personally), so I gave a thought to liberating Java from the grip of it. When at Sun, I looked into having Forth-based firmware replaced with Java-based one -- naturally with a non-SE runtime. It would provide immense benefits (such as interrupt processing). Some were unobvious. Everyone at Sun, except perhaps Ping Lee, considered hacking FCode a career end. Once a manager knows that you are familiar with FCode, you get tasked with it, because everyone else is so keen to avoid it, and that is forever. Your only choice is to go management, or to quit. Replacing Forth with Java would ease this problem considerably... If Mitch Bradley won't like it, tough! It was a pipe dream for many reasons, but a fun one.
It would be great to tackle a project in Java, but with my current work it's hopeless. I can't even complete a 1000-line patch to usbmon for a month.