LibreTorrent is an original Free as in Freedom torrent client for Android 4 and later based on libtorrent. Download and share files directly on your device.

Source code:
https://github.com/proninyaroslav/libretorrent

Implemented features:
- DHT PeX encryption LSD UPnP NAT-PMP µTP
- IP filtering (eMule dat and PeerGuardian)
- Ability to fine tune (network settings power management battery control UI settings etc.)
- Supports torrents with large number of files and big files
- HTTPS and magnet links support
- Support proxy for trackers and peers
- Ability to move files while downloading
- Ability to automatic movement of files to another directory or to an external drive at the end of download
- Ability to specify file and folder priorities
- Ability to select which files to download
- Ability to download sequentially
- Material Design
- Tablet optimized UI