It's simply done in Excel. I was going to install the MS flow chart maker but decided I had enough Micro-Crap software on my machine (and it's not flexible enough).
I need to do something about the tech that is opened up by "Rare Ore Processing" though. I'm not happy with the way it is now. There's a few other minor things to clean up too.
This tech tree is smaller becuase I didn't want to post a huge picture. Anyhow, I'm planning on exporting it to a PDF. I was planning a two page version (as it is now) and version 2. What you see above would actually be on a full sized sheet of paper (in landscape) with the rest of the tech on a second page.
What I'd actually like to do for v2 is expand what I have and include some graphics (i.e. picture of lynx chassis, expanded housing, DIRT, etc.). Like the CIV:CTP posters (if you've seen those). Even though it's not as big, the OP2 tech tree is more complex than CIV (if you can buy that).
What I was looking for in posting all this is if there was anything else you guys wanted to see.
Here's my next list of improvements:
-color coded arrows
-shrink down some of the text so that it all fits in the box
-Plymouth Tech
-Try to create a non-color version (other than black and white) for those of us who don't have color printers
-I think I'm going to separate the "Colony Improvement" color into "Structures" and "Structure Improvement" sections.
-Potentially a list of unit & building stats (separate project?)