This tool provides exercices in formal logic, more precisely for proof systems. You can have a look at the following address: http://pravda.irisa.fr/
Be sure to have installed tsc, the TypeScript compiler.
Run tsc in the root folder.
The release version is then in the folder dist. You may launch it with python -m http.server.
Thanks to Thibaut Antoine for having developed the module for sequent calculus.