I have finally decided to go more deep into math and cs, so to do that I will need proper tool, math tool. Could you please tell me what's the best open source math tool on the web today, since as far as I know majority of good math tools require you to pay for it, which is cool, but I am student and need some open source one and extra cash in my pocket. All are permitted to participate in choosing the best math tool.
Thanks in advance.