PrInS is a theorem prover for first order logic. It's main features are as follows.
If you want to know almost all about it, you can read my PhD thesis. If you want to know all about, you can download it and read the source.
You can download the current version of PrInS here:
Apart from Java, you will need a couple of libraries to compile it:
When you unpack the tar file, you will find two files
README_run, which might be helpful in getting the thing to work.
If you have trouble, feel free to contact me.
PrInS is to be considered in alpha-state. I would not be surprised if you had trouble compiling it. It has undocumented command line flags. The output format is not documented either. On some inputs it just crashes. Also, it occasionally claims to find a proof for something that is wrong. Please let me know if you find any bugs, though!