OSRM GSAK:
An OSRM routing server provided by lignumaqua, for use with GSAK only, less frequent updates, supports car routing
for North-America, Australia and Europe only.
OSRM Public:
OSRM provides a Demo Server to be queried from external users.
They provide a car routing profile only, don't give any guarantees though and expect everyone to adhere to some
rules.
Based on the load on that server, frequent "Too many requests" errors might occur.
XCTrails Routing:
Routing by XCTrails.org is provided free of charge,
but is limited to Foot and MTB and a maximum of 25km per routing leg.
Google Routing:
In order to use google routing (i.e. the
Google Directions API), you need a Google API key.
Depending on your setup and usage, this might result in accrueing potential Google charges!