There are quite a few BitLocker alternatives you can choose from, including TrueCrypt, VeraCrypt, and AES Crypt. Besides these free and open-source BitLocker alternatives, you can also opt for proprietary ones such as Encrypto.
TrueCrypt
TrueCrypt is a full disk encryption program that works on Windows Vista/XP, Mac OS X, and Linux. It owns the following features:
Mounts a virtual encrypted disk created inside a file as if it were an actual disk.
With the pre-boot authentication, TrueCrypt can encrypt the startup partition in Windows.
Automatic, real-time (on-the-fly), and transparent encryption.
VeraCrypt
Based on TrueCrypt, IDRIX designed VeraCrypt as a free disk encryption program. It strengthens the encryption algorithms used for systems and partitions, making them resistant to advanced brute-force attacks.
Offers both GUI & command line for different users.
Highly portable that can encrypt a USB stick or similar with no prior installation.
Strong encryption as well as multiple encryption methods.
AES Crypt
By encrypting files using the Advanced Encryption Standard, AES Crypt is a sophisticated file encryption tool that works with the Windows shell or runs with the Linux command prompt (AES).
Your most sensitive files can be securely encrypted with AES Crypt using a strong 256-bit encryption algorithm. Similar to the BitLocker recovery key, an encrypted file is absolutely useless without a password. You don't have to worry about that someone will read your critical information after it has been encrypted.
Encrypto
Encrypto utilizes AES-256 encryption to safeguard files. Files can be encrypted with Encrypto before being sent to friends or coworkers. Send a file with more protection by dropping it into Encrypto, setting a password, and sending it. Although it's a commercial program, it's still one of the best BitLocker alternatives.