There are a number of existing tools which help with prototyping and playtesting. Here, I examine several of them. Actually comparing them all may prove to be an lifelong task, but I'll keep working on it. Details on the ones I've done are off to the right, and the ones I'm still planning to get to are here:
Of the tools I've already compared, here's the ordered list, according to how well I feel they fit the bill as an easy to use, general purpose prototyping and playtesting tool:
| VASSAL | 79% | |
| ACTS | 70% | |
| LackeyCCG | 67% | |
| ZunTzu | 67% | |
| Battlegrounds Gaming Engine | 63% | |
| Battlegrounds: RPG Edition | 63% | |
| OCTGN | 63% | |
| Taebl | 58% | |
| FlexibleRules | 54% | |
| Board Games Online | 50% | |
| Protohut | 50% | |
| Wildcard | 50% | |
| Thoth Engine | 46% | |
| ScanPlay | 42% | |
| Virtual Board | 42% | |
| Virtual Card Table | 42% | |
| Aide De Camp 2 | 38% | |
| Ditzie | 38% | |
| HexWar | 38% | |
| Sleep Is Death | 38% | |
| CyberBoard | 33% | |
| Magic Workstation | 33% | |
| nanDECK | 33% | |
| O Dream Board | 29% | |
| Apprentice | 25% | |
| Magic Set Editor | 20% |