Some of the calculators below appear in individual posts in a specific context. I have tried not to reproduce existing calculators made by others, such as the excellent ones created by Roy Walter or Concept II.
NOTE: Take these with a grain of salt. Numbers tend to lend an imprimatur of science and precision; there may be less than imagined.
USRowing Handicap Calculator
Training Category Calculator à la Marlene Royle
Training Level Calculator à la Coggan
Training Level Calculator à la Coggan with Visible Watts
Below is the same training zone calculator based on Andrew Coggan's training schema as above, but with the underlying power (watts) information. See relevant post.
Percentage of VO2Max Training Intensity Calculator
This calculates percentage of VO2max intensity based on the assumption that average power (watts) during an all-out 2k effort on the Concept II rowing ergometer approximates 100% VO2max intensity. There is some basis for this assumption. See VO2Max Calculator post.
Ergometer Age Handicap
Age handicaps are rarely used in ergometer events, but you can still find them in the results (e.g., here and here), though you can't always tell what kind of handicap system they used. This 2009 regatta in Michigan used the handicap system below. Not that long ago (2000), the World Indoor Rowing Championhips used a handicap system. The notion behind handicaps is that you can compare rowers independent of age. If the handicap calculation is sensible, you can create meaningful competitions with few people. I don't think these calculations (based on USRowing) are sensible, however. Basically, since ergometer times are faster than water times (for most competent rowers), the handicaps become increasingly out of line (generous) the older you are. I suppose age has (deserves?) its benefits.