What ERP system do tech companies use?

As a SMB tech company, we use our own ERP software (http://www.bluelinkerp.com/). Of course, this is not a privilege other companies may have if the software they provide does not cover their requirements. 

In these cases, many will use disjointed systems focused on specific business functions (i.e. salesforce for their CRM) while others will used an integrated ERP system - especially, the ones that are tried of disjointed systems.

Small-size tech companies can use local or in-house developed applications. Medium size can use open source ERPs like Odoo or SMB or any ERP application that is not designed for large companies like NETSUITE. Large companies can choose Oracle, Dynamics or SAP.