Decal has not been updated because Decal works just fine, and any major update could break existing plugins which nobody would be around to fix.
So instead of adding to Decal itself, it makes more sense just to work on plugins and services which are not part of the core Decal installation. And, people have been doing this.
For instance, Decal Views work poorly. Guess what? A replacement for them already exists, and people are using it right now (
http://www.virindi.net/wiki/index.php/Virindi_Views ). Or maybe you think it would be nice if Decal had a service to let you draw on the radar...well, that exists too (
http://www.flynn1179.net/ac/?radaraddon ). These are things which could have been builtin to Decal, but instead were simply released as additional components. That fact certainly does not mean that development is over.
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Virindi
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****Virindi Plugins FAQ****
http://www.virindi.net/wiki/index.php/Virindi_Plugins_FAQ
http://www.virindi.net - Virindi Tank, Follower, Integrator, Reporter, VCS5, XPHelper, Item Tool, HUDs, etc...
Decal Core Dev -
http://www.decaldev.com