I understand that some poskim forbid using an apple corer on Shabbos, the sort that only removes the core. However I have a corer that slices the apple into eight pieces as well as removing the core at the same time, is this permitted to use on Shabbos or is it borer, and is there a consideration that it is tochain, being done with a specialized tool?
If necessary I can send you a picture of this tool.
It is permitted to use the tool you mention.
Although some prohibited using an apple corer, the reason for this is not strictly on account of borer, because there is always some apple that is removed together with the core, and this can be (and often is) eaten, so that there is no actual problem of borer.
Nonetheless, some prohibit the use of a purpose made tool for separating. In the case of the utensil you describe, the purpose is not to separate but to slice, as well as separating the core. It will therefore be permitted to use the tool.
There is no concern for tochen, because the apple is not being ground or chopped into fine pieces, but only sliced.