Is there an easy, web based, multi player board and card game prototype tester?
An open-source boardgame engine, could be what you are looking for:

Vassal Engine
http://www.vassalengine.org/

It provides counters, cards, board and does not enforce any rules, it provides solely "component handling". You need to create your own module (a container which holds all components as images and text) and then you should be able to send that module to other players or designers to test your prototype. 

You can even play together if the game is multiplayer and not solely solitaire. Play by Forum (PBF), Play by Email (PBEM), Peer-to-Peer (P2P) playing is supported.

Here is a direct link to the user guide to evaluate the features: 
http://www.vassalengine.org/mediawiki/images/8/8c/Userguide.pdf

If you want to get started, you follow these tutorials: 
http://www.vassalengine.org/wiki/Tutorials

Especially: 
http://www.vassalengine.org/wiki/Card_Game_Tutorial 
http://www.vassalengine.org/wiki/Board_Game_Tutorial

While VASSAL certainly is powerful, the initial steps for simple games are quite simple. Yet after a while, the options like automated game setup will be a blessing for you and your playtesters. The game logs will be important to evaluate the game, i.e. find too weak or too powerful strategies.

FAQ for module creation:
http://www.vassalengine.org/wiki/Creating_Modules