Transmission is free software. All its code is freely available online and is licensed under either the GNU Public License v2 or the MIT License.
Changelog
Version 0.2 (11-01-2009)
* Correcting a bug in the event report.
* Adding fields in the WebUI to change the mode.
* Adding a mode to report (downloaded*2) as what you uploaded
Version 0.1 [...]

Changelog 1.9.0: * Bug fix : fixed several problems with parsing some torrent files
* Bug fix : fixed several resource leaks
* Bug fix : fixed startup crash on some systems and added more robust error message for such cases
* [...]

by B4n$h33
Leecher features:
Server Rotation
No-upload
Fake Queue
Share levels
no Share single File
Fakes Tags
Fakes Mods
Nick-Addon Thieves
Dynamic Spread Reask
Dynamic Boost Client
Manual Stuffs
Filter LowID
Auto-Kick System
Upload Management
etc.
Changelog 1.4:
add Auto-Kick Timer [B4n$h33]
add ECR v2 [Spike2]
add Filter some Suspect Bad Uploader [B4n$h33]
add Multi Server Connect [Sarutobi]
add Reset Kad-IP on IP-Change [Spike2]
add ServerAnalyzer [Spike2]
add Show Chunkdots [Slugfiller]
Change Server Rotation Setting [B4n$h33]
Change Slot Controll Code [B4n$h33]
Fixed [...]