The Official Rules, Section I.6, “Ready! Contest Eligibility” states:
“A single competitor or team of competitors may submit a maximum of three submissions. If more than three submissions are received from a single competitor or team, the three most recently submitted will be considered.”
The Software Track sets a limit at two submissions.
When it comes to how many teams you can join, this is separate from the submission rules. Since “A single competitor or team of competitors may submit a maximum of three submissions,” if you are the person submitting on HeroX, you can submit three submissions to Hardware and two submissions to Software. But if you join a team, and there is another person submitting the entry on HeroX, they can have three submissions for Hardware and two for Software. So, you can be the team captain or individual submitter for three ideas on Hardware/two ideas on Software, but you can join multiple teams as a member.