There are thousands of online hate groups and numerous sites that connect them.
There is more than 8 chan to connect violent book burning nazis but here is a smattering of hate groups besides Proud Boys;
Aryan Freedom Network
Atomwaffen Division
American Front
American Nazi Party
Aryan Brotherhood of Texas
Aryan Brotherhood
Aryan Circle
Aryan Nations
Aryan Republican Army
Battalion 14/Connecticut White Wolves[6][7]
The Daily Stormer
Identity Evropa
Libertarian National Socialist Green Party[8][9][10]
Maryland National Socialist Party[11][6]
National Alliance
National Socialist Liberation Front
National Socialist Movement
National Socialist Vanguard
National Vanguard
Nationalist FrontO
Patriot Front
Renegade Tribune
The Right Stuff
Rise Above Movement
The Order
Traditionalist Worker Party
Vanguard America
Nazi Low riders
Vanguard News Network[12][13][14]
Werewolf 88[15][16]
White Aryan Resistance
White Devil Social Club[17][16]
White Order of Thule[18]
Caribbean and South America

and this NPR broadcast https://www.pbs.org/independentlens/blog/who-is-watching-the-hate-tracking-hate-groups-online-and-beyond/

This group vowed to take over the Republican Party in 2018. Identity Evropa
Nationalist Social Club
National States' Rights Party
NSDAP/A