I severly overkneaded my dough (I left it in the standmixer for over 45 minutes by accident). What can I do with this? Can I use it for starter? Any other use-cases? 
In addition to @rumtscho's answer, there is another option: Dough that has active yeast in it can be used as a starter culture for future doughs. This is the method by which bakers used to propagate their yeasts before the advent of readily available dried or pure fresh yeast cultures. It goes under various names, such as poolish, biga and pate fermentee, though technically the poolish is higher hydration than the other two, so yours is more like a biga or pate fermentee. Given that you are just at the kneading stage you would need to ferment ("rise" - though yours won't; it'll just go bubbly) the dough. Then you can simply take some of the dough and add it to a fresh batch of ingredients. The amounts to add vary depending on what you actually want to do with the new bread and how fast you want it to rise. You can also take this and divide it up into smallish amounts; 15 -- 30 ml (0.5 -- 1 oz) works well and freeze, then thaw for usage when needed. Silicone muffin/cupcake trays work well for this, as you can drop the mix in, freeze, then pop-out for storage in a bag. There's some nice instructions here for how to use from fresh. For frozen the process is similar, just make sure that the "dough" is thawed and warm. You will most likely have to play with the amount you use, but given the poor nature of the gluten in your current batch, I wouldn't go over about 25% of the total future bake. 