Terragen 2 is available both as a free download and as a purchase option for Terragen 2 Deep Edition. The free version may only be used for non-commercial purposes and is limited in the following ways:
Render Size Maximum: 800x600
Render Detail Maximum: 1.0
Antialiasing Maximum: 3
Maximum Number of Rendered Populations: 3
Maximum Render Detail for Micropolygon Export: 0.1
You may purchase a commercial license which will remove these feature restrictions. Your license will cover the final release of Terragen 2 Deep Edition and any minor updates (2.x versions)