I want to implement a system that users can sign and send transactions (from their Ethereum account, which -for now- I assume exists) with just a GUI, and maybe asking them to enter their address and password (if necessary, the private key too).
Thanks to @TjadenHess, I found myetherwallet which does what I want to achieve. The GUI involves copy/pasting the generated code, but it's still easier than running
geth (or another software that can connect to Ethereum) and typing the commands manually.
How can I implement such a system? Should I (my application) be running the software on a remote server and let people use it for a while, or should I ask/help them to install the necessary software (as part of my application, like Ethereum Wallet does with geth) on their devices and generate and execute the commands for them?
Is any of these options possible? If so, I would much appreciate any directions on how / where to implement such a system.