Are you looking for an existing mod or do you want to program your own? In the first case I'd recommend you try E+
+1
-----------
TRiLLeNNiuM, if you do try E+, make sure you get the download from here:
http://oa.goquake.com (The Official Site for E+ on OA).
Two tips: Since you seem interested in modifying weapons and possibly things like physics, damage, knockback, etc., please be sure to take a good long look at the default.cfg file and then use it as a template to design your own Game Style Config. It's sad when E+ Admins just use the configs that I or others design. The beauty of E+ is in its scripting system which opens up everything for Modification.
Second, seriously consider not using custom maps. Personally, I love them and won't change. But, not using them will bring some additional players to your server as E+ can be played Server Side Only (i.e., without the Mod) and with Auto-Downloads disabled. Furthermore, if you use custom maps you will probably need a Q3A/Q3TA texture pack since OA doesn't have good q3 texture support and isn't scheduled to until OA 3.