My hobby is to answer questions about GAP (http://www.gap-system.org/, Twitter:@gap_system), a system for discrete computational algebra. There is a tag (gap) at the Mathematics Q&A site to label such questions, and also some suggestions on using this tag. If any of the two proposals for Q&A sites for Sage or for Computer Algebra Systems will reach beta stage, I would also be interested in answering GAP questions asked there.
Before asking about GAP at Mathematics Q&A site, please note that there are well-established support channels for GAP users such as GAP Forum and GAP Support where your question might be noticed quicker by a larger number of GAP users and developers of GAP and its packages; therefore, dependently on your question, GAP Forum and GAP Support may be more suitable places for posting it.
Note that it may also happen that your question is already answered in the Frequently Asked Questions section of the GAP website or in the GAP Forum (to search GAP Forum archives, click here).