We present thermodynamic studies of a new spin-1/2 antiferromagnet containing undistorted kagome lattices---barlowite Cu$_{4}$(OH)$_{6}$FBr. Magnetic susceptibility gives $theta_{CW}$ = $-$136 K, while long-range order does not happen until $T_{N}$ =
15 K with a weak ferromagnetic moment $mu$ $<$ 0.1$mu_{B}$/Cu. A 60 T magnetic field induces a moment less than 0.5$mu_{B}$/Cu at $T$ = 0.6 K. Specific-heat measurements have observed multiple phase transitions at $T ll$ $mid$$theta_{CW}$$mid$. The magnetic entropy of these transitions is merely 18% of $k_{B}$ln2 per Cu spin. These observations suggest that nontrivial spin textures are realized in barlowite with magnetic frustration. Comparing with the leading spin-liquid candidate herbertsmithite, the superior interkagome environment of barlowite sheds light on new spin-liquid compounds with minimum disorder. The robust perfect geometry of the kagome lattice makes charge doping promising.
