List of alternative ARM TEE implementations:

FREE - Open-source implementations:

• OP-TEE, an open source implementation from STMicroelectronics under BSD license
• TLK (Trusted Little Kernel - PDF Overview), an open-source implementation from Nvidia under BSD license
• T6, and open-source implementation and research topic under GPL license
• Open TEE, an open source implementation and research project from the University of Helsinki and sponsored by Intel. Provided under an Apache license. Open TEE is a virtual, hardware-independent TEE implemented in software. Open-TEE conforms to GlobalPlatform specifications. It allows developers to develop and debug trusted applications with the same tools they use for developing software in general. Once a trusted application is fully debugged, it can be compiled for any actual hardware TEE

PAID - Commercial implementations:

• t-base, a commercial implementation from Trustonic that has been qualified by GlobalPlatform
• QSEE - TrustZone implementation by Qualcomm - mostly targeting phone manufactures, used in most phones that are based on Qualcomm Snapdragon SoC - for example Nexus 4, Nexus 5, LG G2, HTC One series, Moto X, Samsung Galaxy S4, and Samsung Galaxy Note 3
• securiTEE, a commercial implementation from Solacia that has been qualified by GlobalPlatform

DUAL - Implementations with dual commercial/open-source licensing:

• SierraTEE by Open Virtualization / Sierraware available both under commercial and GPL-licensing