CZ.NIC which is known thank to popular and safe Turris Omnia router, introduced a new modular router which is called Turris MOX.
MOX is modular and open-source router where you can just buy only modules which you need.
There are a few modules which you can order on Indiegogo. Each module is connected by connector.
The main module is Turris MOX A, also called like Basic module, which is main part of all variants of Turris MOX.
The board contains USB3.0, microSD slot for OS and GWAN port.
The first module is Turris MOX B (Extension module) which contains mPCIe slot with 5GHz WiFi. If you don't want to use 5GHz WiFi, you can connect SSD and the MOX can be used like NAS.
Or you can connect LTE module and SIM card and the MOX is LTE modem.
Turris MOX C (Ethernet module) includes 4x GLAN port.
Edit: E module (Super ethernet) was added to list of modules. The E module includes 8 ethernet ports and you can combine that with another (also ethernet) modules. [Source]
The last modul is Turris MOX D (SFP module) where you can use it for connecting of optical fiber cable.
Each board you can buy for 29 USD and the release of modules will be on October of 2018.
The operating system for MOX is Turris OS which is based on OpenWRT.