Everything you need and nothing you don't. Transmission includes critical features such as a block list function, global bandwidth limits, speed limits, NAT & manual port assignment, Remote desktop management, Seeding and Queue limits (I suggest stop seeding at ratio: 2.00 or a greater ratio) , and the ability to call a script when a download completes. In short, it works out of the box with little to no configuration, but has power and features should you want to set them/ utilize them.

Transmission-gtk uses only 17 mb of RAM in idle state and 24 mb in download state.

Transmission is free, ad-less and open source software licensed under GPL with parts under MIT with source code available here. Being open source allows anyone to check if the software has no malicious code, is secure and respects privacy.

Transmission is great for getting things done without looking too much under the hood. It still has advanced options, they're just tucked away from sight.

Not officially available on Windows, but there is a port, making for a good app to use for those that use multiple OS's.